Niger's government has been dissolved after a majority in parliament backed a no-confidence vote.
Mr Amadou had been prime minister of Niger for seven years
Some 62 delegates in the 113-seat national assembly voted Prime Minister Hama Amadou's government out of office.
Opponents accused the government of complicity in a corruption scandal involving the embezzlement of education funds primarily from foreign donors.
Mr Amadou denies wrongdoing. President Mamadou Tandja must decide whether to name a new PM or call elections.
Speaking after the vote, Mr Amadou, who had been in office since 2000, said: "Niger's democracy has made itself heard".
"After four no confidence votes, today my government has fallen," he said.
The corruption affair, in which some $9m of European Union aid was allegedly taken between 2002 and 2006, led to the detention of two former education ministers last year.
The BBC's Idy Baraou the capital, Niamey, says the opposition MPs were angered by Mr Amadou's refusal to attend a parliamentary investigation into the affair.
General secretaries within the ministries are now running government affairs and by law the president needs to appoint a new prime minister or call an election within a few days.
But as one of the poorest country's in the world, the president is unlikely to want the expense of an election, our correspondent says.