In a letter printed in the Ugandan newspaper Daily Monitor, Tutu urged Ugandan members of parliament to vote against the Anti-Homosexuality Bill that goes to vote later this month.
"Should the Anti-Homosexuality Bill be voted into law, it will criminalise acts of love between certain categories of people, just as the apartheid government made intimate relations between black and white South Africans a punishable offence," wrote Tutu.
The proposed legislation has been called the "Kill the Gays" bill in Ugandan media. In previous versions of the bill, homosexual relationships were divided into two categories, namely "aggravated homosexuality" and the "offence of homosexuality".
It was proposed that people convicted of "aggravated homosexuality" - that is, an HIV-positive person or a "serial offender", or a person who has homosexual sex with a minor or someone who is disabled - should face the death penalty.
Those convicted of " the offence of homosexuality" face life in prison.
Parliamentarian David Bahati, the author of the bill, said last month that legislators had "moved away from the death penalty after considering all the issues that have been raised".
"There is no death penalty," he said.
Bahati said the bill now focuses on protecting children from gay pornography, banning gay marriages, counselling gays, as well as punishing those who promote gay culture. Jail terms are prescribed for various offences, he said, but offered no further details.
Tutu also took a swipe at the ANC on Saturday at a Cape Town event to honour the late struggle hero Kader Asmal. Heasked a small group of former apartheid activists: "What have we become?"
Tutu told Minister in the Presidency Trevor Manuel: "You don't belong in this government."
He slammed the state of education, specifically the failure to deliver textbooks in Limpopo earlier this year. He was also outraged at the tax-funded upgrades made to President Jacob Zuma's private residence in Nkandla, KwaZulu-Natal.
"Who in their right minds could have approved the expenditure of more than R200-million?
"And to do it in that area, where you have this nice place standing up and, just around [it], squalor and poverty," said Tutu.
"Trevor, you tell your boss this old man who said he was retired, I am going to come back. You tell him that this old man is now going to pray like he prayed for the Nats (the National Party), to come to an end." - Additional reporting by Sapa