Karin Smirnov or Smirnoff (née Strindberg; 26 February 1880 – 10 May 1973) was a Finno-Swedish writer. She was the daughter of August Strindberg and Siri von Essen.

Smirnov was a socialist; she married Russian Bolshevik Vladimir Smirnov [sv]. She wrote plays and also books about her mother and father, and their marriage. She lived in Finland from 1893 to 1918 and in Sweden from 1918 onwards.