Mandela said he identified with the main character of the film, a young gangster.
As a teenager in South Africa's rural Transkei region, Mandela herded livestock. He and friends would use the dregs of locally brewed beer to lure pigs from the village, the BBC reported.
Once they were far away, the boys would stab, roast and eat the pigs, he said.
"Some of the leaders of this country and elsewhere in the world started with misdemeanors of all kinds, but as they grew up, they became responsible people who have served our country very well," Mandela said.
Mandela thanked the makers of "Tsotsi" for putting South Africa "on the map," but film director Gavin Hood responded that it was Mandela himself who had done this.
"Without what you did, we would not have been able to make this film together as South Africans in a free country," Hood said.