"I thought the president gave a superb address [at Thursday's interfaith service] to the people of this city and the state and the nation," Romney, a former Massachusetts governor, told CNN Thursday. "It was an inspiring day."
Romney was invited to attend Thursday's service at the Cathedral of the Holy Cross by Democratic Gov. Deval Patrick, who also invited other current and former Massachusetts dignitaries.
Romney said he and Obama did not speak at the event.
In the interview, Romney stressed the need to learn everything possible from Monday's bombings in which three people were killed and more than 170 people were injured.
"This is a learning opportunity," Romney said. "We should learn the lessons that come from this and apply them to the extent that we possibly can."
Asked why he thinks bad things happen to good people, Romney said his only response to this type of question was praying for comfort and understanding.
"I believe very deeply that we have a creator and that he loves us and cares for us," said Romney, a Mormon. "But when he actually intervenes in the affairs of the people on this earth -- it's something that happens only rarely -- and when that happens and why that happens and who that happens to is something that we don't understand."