The incumbent President said his rival had won a "narrow victory"
Mongolia's opposition party candidate has won the presidential election.
The leader of the Democratic Party and two-time former prime minister, Tsakhiagiin Elbegdorj, had campaigned on an anti-corruption ticket.
Incumbent President Nambaryn Enkhbayar - of the former Communist party - admitted a "narrow" defeat. Official results are yet to be released.
The election campaign was dominated by the issue of distributing the country's vast mineral wealth.
President Nambaryn Enkhbayar admitted defeat in Sunday's poll, saying he respected the result, according to Chinese state media.
He said that, according to parties' counting of the votes, Tsakhiagiin Elbegdorj - his only rival in the election - had won a narrow victory.
Mongolian media are also reporting that Mr Elbegdorj has won.
Speaking earlier, the Democratic Party chairman told supporters that Mongolia was "meeting a new morning, with a new president".
The BBC's Quentin Sommerville in Beijing says there were fears that a close result could lead to civil unrest.
Allegations of vote rigging during last year's parliamentary poll sparked protests in which five people died and hundreds were hurt.
Reports from the capital Ulan Bator say that the streets are calm but police and troops are on stand-by in case of trouble.
In 1990, Mongolia abandoned its 70-year-old Soviet-style one-party state and embraced political and economic reforms.
Democracy and privatisation were enshrined in a new constitution, but the collapse of the economy after the withdrawal of Soviet support triggered widespread poverty and unemployment in the sparsely-populated, landlocked country.