More than half of the 14.5 million eligible voters took part in the vote, officials said. Of those, 89.4 percent voted in favor of the new constitution, Interior Minister Maj. Gen. Mohammad Ibrahim al-Shaar told the official Syrian Arab News Agency.
The minister praised the high turnout despite threats by "armed terrorist groups" in the country.
The constitution would impose a seven-year term limit on the president. There is no mention of the ruling Baath Party in the draft document.
Syria is on the cusp of civil war nearly a year into an uprising against Syrian President Bashar Assad. The United Nations estimates at least 6,000 people have died in the uprising, noting high-ranking government officials are likely committing crimes against humanity in the country.
Members of the United Nations are divided over how to respond to the crisis. Russia and China have objected to foreign interference, prompting Western powers to tighten economic sanctions in Assad's regime.
The International Committee of the Red Cross said Monday it gained access to Hama for the first time since mid-January. The ICRC and Syrian Red Crescent are working with the opposition and the government to evacuate those wounded during the conflict.