Katja Fain (born 31 August 2001) is a Slovenian swimmer. She represented Slovenia at the 2019 World Aquatics Championships held in Gwangju, South Korea. She competed in the women's 200 metre freestyle and women's 400 metre freestyle events. In the 200 metre event she did not advance to compete in the semi-finals and in the 400 metre event she did not advance to compete in the final. She also competed in the women's 400 metre individual medley event.