A fundamentalist church pastor had sex with two of his teenage daughters to educate them on how to be good wives, a South Australian court has heard.

The 54-year-old man, who cannot be named, was today sentenced in the SA District Court to eight and a half years jail after pleading guilty to seven counts each of incest and unlawful sexual intercourse.

The court heard that the man had sex with his daughters for nearly a decade from 1991 when they were aged 13 and 15 at the family property.