The 32-year-old has convinced inmates - including a feared gang leader - to join the sessions at Pretoria's Atteridgeville Correctional Centre, Henke Pistorius told The Times newspaper.
Mr Pistorius, 62, said: "They are hard-core chaps, the problem people in the prison, but now they are all meeting to follow the Bible once or twice a week.
"Oscar leads the studies and is able to accommodate those who aren't so familiar with the Bible, to explain the meaning of all the verses."
The double leg amputee, who has spoken publicly about his Christian faith, was sentenced in November 2017 to 13 years in prison for killing Reeve Steenkamp at his home in 2013.
Oscar Pistorius shot the graduate and model multiple times through the locked door of his bathroom. During his trial, Oscar Pistorius said he thought the property had been broken into.
Henke Pistorius continued: "I have no doubt that Oscar has changed the environment in the prison for the better.
"He is helping to mediate between people and is having a positive influence."
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.