"Large numbers of people turned out from the countryside and gave us much needed support. The combined countryside and city numbers means that we have probably won the election," he said.
The MPRP said that the rival Democrats had taken 21 seats, while three other parties won one seat each.
Votes on eight other seats were still being tallied.
The General Election Committee, who must formally declare the winner, said that the MPRP's announcement was premature.
"The parties are announcing unconfirmed numbers and they are celebrating too early," Purevdorjiin Naranbat, an election committee official, said.
"The numbers are still coming. Maybe we will make a formal announcement tomorrow [Tuesday]."
Many voters in the recent poll expressed a desire for Mongolia's future to see a more stable government.
The election of a new political party is expected to kick-start mining legislation and business contracts left over by the outgoing parliament.
With inflation running at 15 per cent, the economy is seen as the main issue, outstripping unemployment and corruption as a concern for Mongolians.
More than 350 candidates from 12 parties and one coalition ran in the State Great Khural election, officials said.
The MPRP, a former communist party, is Mongolia's oldest. It ruled Mongolia from 1921 until 1996, when it was beaten by the Democratic Party.
However, they disagree over whether the government or private sector should hold a majority stake of the country's mineral deposits.
The instability held up economic reforms and shook investor confidence, but the nation's economy still grew by 9.9 percent last year thanks largely to its vast deposits of copper and gold.