Mr Alexis (R) became prime minister of a coalition government in 2006
The Haitian Senate has voted to dismiss Prime Minister Jacques-Edouard Alexis following widespread rioting earlier this week over soaring food prices.
A special session of the upper chamber backed a motion calling on President Rene Preval to appoint a new cabinet.
The vote came shortly after Mr Preval announced an emergency plan to reduce the price of rice by more than 15%.
In the capital, Port-au-Prince, the scene of deadly food riots earlier, a UN peacekeeper from Nigeria was killed.
A UN spokeswoman in Haiti said the soldier was shot dead Saturday afternoon, but that UN troops had not returned fire.
At least five people died in the riots over food prices earlier this week.
Haiti is one of the poorest countries in the world. Most Haitians earn no more than $2 a day, and they have struggled to feed themselves as the prices of rice, beans and fruit have risen by 50% in the last year.
Earlier this month, UN Secretary General Ban Ki-moon warned that the food crisis threatened the Caribbean nation's fragile security.
President Preval appointed Mr Alexis as prime minister of a six-party coalition government in May 2006. He had survived a no-confidence vote in February over his handling of the economy.
Reflecting widespread public anger at the rising cost of basic foodstuffs in the country, 16 of Haiti's 27 senators said they had no confidence in Mr Alexis's government and instructed the president to appoint a replacement.
"Now it's my turn to play," Mr Preval said when he was told by journalists of the vote against his ally, according to the Reuters news agency.
On Thursday, opposition senators warned the president that his proposals would "not solve the immediate problems of the population" and were "too little, too late".
"It is obvious that the majority of the people don't believe any more in the capacity of your government to take courageous measures to ease the misery that the population is facing daily," they wrote.
Saturday's vote of no-confidence came shortly after Mr Preval announced a 15.7% reduction in the price of a 23kg (50lb) bag of rice from $51 to $43.
Haitians ran through the streets protesting against high food prices
After meeting food importers at the National Palace in Port-au-Prince, the president said $3 of the price cut would be paid by the private sector and the rest funded by money from international donors.
"The situation is difficult everywhere around the world, everyone has to make a sacrifice," he told a news conference.
"We are not going to lower taxes on food," he added, reiterating the government could not afford to cut revenues because it would not have enough money to pay for longer term projects to create jobs and boost agriculture.
Mr Preval made a national address on Wednesday saying the riots over food price increases earlier this week were "not going to solve the problem".