The private ceremony was held in the Blue Room of the White House. Obama and Vice President Joe Biden will take their public oaths Monday in front of the Capitol before a crowd on the National Mall in Washington.
Unlike the president's 2009 inaugural oath, Obama spoke clearly and without stumbling over the words.
First lady Michelle Obama, and daughters Sasha and Malia stood by Obama's side during the oath.
Obama was sworn in using the Robinson family Bible, which was held by the first lady.
"The bible was a gift from the first lady's father, Fraser Robinson III, to his mother, LaVaughn Delores Robinson, on Mother's Day in 1958. Mrs. Robinson was the first African American woman manager of a Moody Bible Institute's bookstore; this was the only Bible she ever used," the presidential inaugural committee media guide said.
Once his oath was spoken, Obama said "All right, thank you everybody," and exited the room.
Earlier in the day, Obama and his family attended a pre-inaugural church service in which his re-election theme of moving forward was related to the story of Moses.
The Rev. Ronald E. Braxton of the Metropolitan African Methodist Episcopal Church read from the book of Exodus Sunday. He urged Obama to not let obstacles interfere "where forward is the only option."
"I'm a witness that the God of Moses , with miraculous power, still moves on behalf of humankind," Braxton said. "Forward was the only option."
Biden officially sworn in for second term
WASHINGTON, Jan. 20 (UPI) -- U.S. Vice President Joe Biden was sworn into his second term Sunday, one day before he and President Barack Obama take their public oaths.
Just after 8 a.m., Associate Justice Sonia Sotomayor administered to Biden the oath of office at the Naval Observatory, his official residence. Sotomayor is the first Hispanic and fourth female judge to administer an oath.
Biden was sworn in using the Biden family Bible, which is five inches thick and has a Celtic cross on the cover. Biden used the Bible each time he was sworn in as a U.S. senator and when he was first sworn in as vice president in 2009.
Just prior to reading the oath, the Rev. Kevin O'Brien offered a prayer, per the request of Biden and his family.
"Gracious God, at this moment in our history, we ask your blessing on your servant, Joseph, as he renews his sacred pledge to his country. Amid all the complexities of our world, a world so beautiful but also broken, give him a share of your wisdom so that he can know what is good and give him the courage to always do what is right," he said.
"Walk close by him so that he can do justice and to labor tirelessly for a more just and gentle world. Empower him to be a voice for those without a voice, for those on the margins, those so easily overlooked, for you will judge us all by how we care for the least among us."
Biden personally selected Sotomayor to administer the oath.
"It's an incredible honor to have Associate Justice Sonia Sotomayor swear me in," Biden said in a statement prior to the ceremony. "I believed strongly that she would make a great Justice, and it was one of the greatest pleasures of my career to be involved in her selection to the court."
Sotomayor left immediately after administering the oath. "She has to leave right now," Biden told the 120 guests gathered at the event. He said she was due in New York. "So I apologize, we are going to walk out, her car is waiting, so she can catch a train I hope I haven't caused her to miss," he said.
Biden and his family and friends celebrated mass prior to taking the oath.
After the ceremony, Biden joined Obama at Arlington National Cemetery for a traditional wreath-laying ceremony.
Obama and Biden will take their public oaths Monday in front of the Capitol before a crowd on the National Mall.
Algeria hostage death toll could rise
IN AMENAS, Algeria, Jan. 20 (UPI) -- The Algerian government warned Sunday that the death toll after a deadly siege where at least 23 hostages died could increase after further investigation.
The Saturday raid ended a four-day hostage situation at a natural-gas plant where hundreds of people were being held. Citing military sources, Algerian state news said at least 685 Algerian workers and 107 foreign nationals were released during the siege.
Algerian officials initially put the death toll at 23 hostages and 32 terrorists, but that number could increase, The New York Times reported. Hostages from the United States, Japan, Norway, France and Britain are among the dead or unaccounted for.
Leaders across the globe have condemned the attack, for which al-Qaida-linked Mokhtar Belmokhtar has claimed responsibility, The Financial Times reported.
"We have had successes in recent years in reducing the threat from some parts of the world, but the threat has grown particularly in North Africa," said British Prime Minister David Cameron.
"This is a global threat and it will require a global response. It will require a response that is about years, even decades, rather than months. It requires a response that is patient and painstaking, that is tough but also intelligent, but above all has an absolutely iron resolve and that is what we will deliver over these coming years," he added.
The hostage-takers, identified as Islamic militants, stormed the plant last week in apparent retaliation for France's intervention in neighboring Mali. The attackers claimed to be from a group called Signers in Blood and said they were convinced Algeria would assist the French in their Mali campaign, The New York Times reported.
Myanmar army attacks rebel base
LAIZA, Myanmar, Jan. 20 (UPI) -- Officials said the Myanmar army has begun an attack on Kachin rebel forces, breaking a short government ceasefire that began Friday.
The BBC said Myanmar troops attacked a Kachin base near Laiza, which is near the Chinese border in the northern area of Myanmar. Hundreds of government troops hit the base with mortar and artillery fire.
If the base falls, it will likely be easy for the Myanmar military to take Laiza, which would likely force thousands of civilians to flee, the BBC said.
The Kachin Independence Army, the only major ethnic group that hasn't signed a long-term ceasefire with the government, are fighting for ethnic Kachins to take greater control of northern Myanmar.
Although the Myanmar government has pledged to resolve the conflict, the army began a new offensive last month.