St Katherine of Alexandria was one of the highly venerated martyr saints in medieval Scandinavia, Estonia and Finland. Her cult was promoted especially by the Dominican order. In my paper, I shall present the many-layered traditions centered around St Katherine. I shall discuss one of the most important sources of her martyr legend, by Jacobus de Voragine (13th c,), and track the traces of her legend in Finland and Estonia. I am asking, how St Katherine was interpreted in Finnish and Estonian folklore and ritual traditions, and paying attention to the songs about St Katherine in Finnish: Kalevala-metric song about the death of Katherine, and a rhymed ballad called Pieni Katri, "Little Katri". I shall also analyse the ritual traditions on Katherine, who has been venerated as a women's saint and promoter of the welfare of the cattle and sheep. The Estonian mumming traditions with songs, and the importance of Katherine as a protector of sheep, "lambajumal" is discussed, as well as the connection of this tradition with Finland.