The group said Cameroon should drop its laws against homosexuality.
The two prisoners, who were given the maximum sentence, and a third man who jumped bail were arrested in July. Police said they had been caught having sex in a car.
"The Yaounde court must overturn this shocking sentence, which punishes these three men solely on the basis of their perceived sexual orientation," said Erwin van der Borght, Amnesty International director for Africa. "People accused of such crimes in Cameroon often face abuse and violence from other detainees or prison officers in detention. The two men must be released immediately and the Cameroonian authorities must repeal the country's discriminatory anti-homosexuality laws."