A former Christian Brother who sexually abused six vulnerable boys at a Victorian orphanage has been jailed for more than 12 years.

William Stuart Houston, 77, abused the boys, aged 10 to 14, when he was their supervisor at Geelong's St Augustine's Orphanage in the 1960s.

Former Christian Brother William Houston in 2002. Credit:Channel Nine

Victorian County Court Chief Judge Peter Kidd says the boys were powerless to stop Houston's offending and each was especially vulnerable.

"They were wards of the state. They were young and they were under your control," the judge told Houston on Tuesday. "You were fully cognisant of this vulnerability."