"Duduzane, I've not heard..that he has ever benefitted, his business that he's involved in from government. Never, I've never done that," Zuma said while answering questions in the National Assembly.
"His involvement in business is in his own accord....there is no law that says he cannot get involved in business."
Maimane had asked Zuma whether he was ready to concede that he has failed other youth, while helping his son along in his business ventures.
Zuma scoffed at the questions, saying unemployment was not caused by his son and his business interests.
"You just being funny to a young man who has gone to school, capacitated himself and is now in business," the president said in defence of his son.
"You are isolating a young man in South Africa simply because he is the son of a president...I'm saying its unfair to the young man."
Duduzane Zuma together with business partners, the Guptas, have several mining interests in South Africa.
Allegations have been raised in both the Public Protector's report into state capture, as well as a trove of leaked emails, that government and state-owned entities have been giving the Guptas, the Indian-born family who are friends with the president, preference when handing out lucrative contracts.
African News Agency