With all 26 constituencies counted, preliminary results showed the former army general secured another five-year term with 94.4% of the votes cast in Sunday's nationwide poll, the Interior Ministry said.
Final results were due later on Monday.
The remainder of the votes were split between small opposition parties' candidates Muhammad Buchiha, Munir Beji and Muhammad Ali Haluani.
It was the second presidential election open to multi-party politics since independence from France in 1956 and voter turnout exceeded 90%, the preliminary results showed.
Bin Ali, 68, came to power in 1987 after the peaceful removal of president-for-life Habib Burqaiba, the father of modern Tunisia, after he was declared senile and unfit to rule.
Bin Ali has since won three presidential elections with more than 99% of the vote, all criticised by rights groups.
Opposition parties and rights campaigners attacked Sunday's presidential and legislative polls as a farce to disguise a police state that keeps control by beating dissidents, jailing
hundreds of political prisoners and censoring the media.
Diplomats said they would consider a slight dip in support for the president to indicate that Tunisia, which draws millions of tourists from Europe, was showing signs of opening the democratic tap slightly.
Tunisia's rights group was not
allowed to monitor polls
Tunisia, a US ally in the "war on terror", has cracked down on domestic opposition groups. The US administration has been stressing greater reforms in the country.
Bin Ali remains popular at home for boosting the standard of living, literacy, economic growth at five per cent for the past decade and giving women more rights than in most other Arab countries.
"I voted for Bin Ali because he saved my country from big trouble in the past. With him I am happy and my children have been to school and got jobs," said Belgacem Hanachi, 72.
The ruling Constitutional Democratic Rally (RCD) again won control of parliament in Sunday's vote.
The Democratic Progressive Party, the main opposition party, pulled out of the poll, citing unfair conditions, but the pro-free market government rejects the charges.
"Our information indicates no massive voter turnout. There are some irregularities, like officials urging voters to back bin Ali and the RCD"
candidate Muhammad Ali Haluani
Muhammad Ali Haluani, the only candidate to openly criticise the head of state, said the results were a foregone conclusion but he believed his effort would stimulate some democracy.
"Our information indicates no massive voter turnout. There are some irregularities, like officials urging voters to back bin Ali and the RCD," he said.
Tunisia's independent human rights group was denied permission to monitor the polls. The Arab League observed at a few polling stations.