The proposals shift power from the president to the national parliament and set the stage for a general election in September.
Last night, Roza Otunbayeva, the interim leader, claimed the proposals had been approved, despite no official result, and said they would give her government legitimacy.
"The new constitution has been adopted, despite the savage attacks of its opponents," she said. "The people have put a full stop on the epoch of authoritarian, nepotistic management. Today we reached victory on the path to a true government of the people."
The new constitution will make the country Central Asia's first parliamentary democracy, remove immunity from the president and reduce her powers.
It will also bring legitimacy to the interim government, a coalition of opposition forces who stepped in after former President Kurmanbek Bakiyev was toppled by riots.
The authorities pressed ahead with the vote despite bloody clashes between minority Uzbeks and majority Kyrgyz earlier this month that sparked fears the country faced collapse. Mrs Otunbayeva, the country's interim leader, travelled to Osh, one of the most volatile areas, to cast her vote.
"We will show the world that Kyrgyzstan is united," she said. "We want to heal ourselves from the pain that struck as a result of the tragic events."
The referendum saw a turnout of over 65 per cent and was carried out with few reports of violence, despite fears of international agencies, who warned that the vote could tip the country back into ethnic bloodshed.
Military police and civilian volunteers kept a close guard on the streets of Osh and Jalalabad, the towns at the centre of this month's ethnic violence, which saw up to 2,000 killed.
The result is a major victory for Ms Otunbayeva, a former soviet diplomat who served as the country's first ambassador to Britain.
She was declared president in April by the coalition of opposition leaders, who stepped in to rule after former President Kurmanbek Bakiyev was toppled by riots in the country's capital Bishkek.
Mr Bakiyev spoke from exile in Belarus to dismiss the referendum and the leader who replaced him, saying her behaviour was "frivolous and irresponsible".
"She is leading the country into a dead end," he said. "A strong president acts more swiftly."
International agencies last week warned that Mrs Otunbayeva's refusal to delay the referendum risked causing a return to the violence that was still raging less than two weeks before the vote. Human Rights Watch said the referendum threatened to make the situation "even more volatile" while International Crisis Group urged the government to reconsider holding the poll.
The situation in Osh remained tense during Sunday's vote. Citizens were brought to vote in protected bus, the Organisation for Security and Cooperation in Europe pulled back its planned 300 observers on safety grounds, and the curfew in the city, lifted briefly for the vote, was reimposed just an hour after booths closed.
Muzaffar Saipov, an ethnic Uzbek in Osh, was sceptical that the referendum would give the town a new start.
"I'm sure that people still will be afraid to go outside their homes," he said. "Soldiers are acting on their own, doing whatever they want, and people are afraid of them. It will take time: not a week, but maybe a month, or half a year."
