Kerstin Martha Tidelius (born 14 October 1934) is a Swedish actress.
Born in Stockholm, she worked mainly on stage with a total of about 20 film and TV appearances.
Her most notable performances are Ingrid Löfgren in the long running Swedish TV series Hem till byn and a supporting role as Henrietta Vergérus, the bishop's sister, in Fanny and Alexander by Ingmar Bergman.
She was awarded the Svenska Dagbladets Thaliapris (the Thalia Acting Award) in 1966.