The Mongolian People's Revolutionary Party, the former Communist party now known as MRRP, was voted out in 1996 but re-elected in 2000, and now appears to be riding new popularity.
Its candidate, Nambariin Enkhbayar, received 53 percent of votes cast on Sunday, said J. Yadamsuren, chairman of the Federal Election Commission - above the 50 percent minimum required to avoid a runoff election against any of Enkhbayar's three rivals.
His victory came amid nostalgia for the stability of one-party rule and Soviet subsidies that halted in 1990, and his own promises to end chronic poverty in this sprawling, sparsely populated nation of 2.5 million people wedged between Russia and China.
''All the candidates sounded the same to me, so I just voted for my old party,'' said 62-year-old Batsukh Tseveenchimed of the MPRP.
Mongolia has a parliamentary system, with a government run by a prime minister. But the presidency has grown in importance as the country went through a series of governments over the past decade.
The MPRP's rivals complain that the party still dominates election bodies that register voters and run polling stations. Foreign observers were visiting polling stations on Sunday, but there were no immediate reports of misconduct.
Government radio said turnout was more than 70 percent - low by Mongolian standards. It wasn't clear if the number reflected voter apathy following repeated changes of government and protests over claims of official corruption.
Turnout was 83 percent the last time Mongolians voted for president in 2001, and in other elections is usually above 80 percent.
Enkhbayar, a former prime minister, campaigned on a promise to do more to attract foreign investment.
The second-place candidate, Mendsaikhanin Enkhsaikhan of the Democratic Party, drew his support from anti-communists and defied police to take the streets in 1990 and bring down one-party rule in this country. Enkhsaikhan won 20 percent of the vote.
The Republican Party's Bazarsadyn Jargalsaikhan, one of the country's richest men, won 14 percent of the vote.
The Motherland Party's Badarchyn Erdenebat - who supported a national referendum to give more power to the presidency in a country where parliament is splintered among many parties and the prime minister changes frequently - won 11 percent of the vote.