Over 30 close associates of Colonel Gaddafi were tried for suppressing peaceful protests during the uprising, reported BBC.
Saif al-Islam had appeared at hearings by video-link, as he was captured - in the town of Zintan, which is fighting Tripoli-based brigades in the country's civil war. He is being held by a former rebel group from the town of Zintan that refuses to hand him over.
Others who were sentenced appeared in person, having been extradited from neighbouring countries to Tripoli before security collapsed in Libya.
Saif al-Islam also wanted by the International Criminal Court on charges of war crimes and crimes against humanity.
The trial, which opened last year, has been dogged by criticism from human rights agencies, who are concerned about the fairness of Libya's judicial system.
They have the right to appeal against their sentences within 60 days.