A South Australian man will spend at least two years in jail for bashing a grandmother unconscious and grabbing his young daughter from her.

The Adelaide District Court has been told the woman has permanent brain damage and cannot remember who her grandchildren are.

Benjamin John Koch, 38, says the woman insulted him during an argument last August at Mount Gambier over his relationship with her young daughter.

Koch pushed the woman to the ground and punched her several times, then kicked her in the head in a bid to silence her moaning.

He then kidnapped his 10-month-old daughter the woman had been babysitting.

Koch was given a jail sentence of four-and-a-half years with a non-parole period of two years and three months.