A South Korean Christian pastor was jailed for 18 months for having a decade-long affair with a woman whose wedding he had officiated at, a court said Saturday.

Adultery in South Korea is a criminal offence punishable by up to two years in prison but most offenders usually receive only suspended jail terms and imprisonment is quite rare.

The 51-year-old pastor, whose name has been withheld for privacy, had a secret affair with the woman, 41, for more than 10 years after conducting her marriage ceremony. She and her husband were both followers of his church.

The woman was also given a year-long jail sentence.

"The pastor, who officiated at the couple's wedding, should have prayed for their happy marriage life," the court in central city of Cheongju said in a statement.

"Stern punishment should be meted out to the accused who greatly disturbed basic social order and left bitter feelings of betrayal among many others."

The court handed out the jail sentences on Friday.

The adultery trial started after the husband pressed charges against his wife and the pastor. The couple have subsequently been divorced. (AFP)