Kajetan "Kai" Mühlmann (26 June 1898 – 2 August 1958) was an Austrian art historian who was an officer in the SS and played a major role in the expropriation of art by the Nazis, particularly in Poland.
He worked with Arthur Seyss-Inquart in the initial Nazi government in Vienna following the Anschluss, in the General Government (occupied Poland) and in The Hague where he headed an art clearing house in the occupied Netherlands known as the Dienststelle Mühlmann (Mühlmann Agency).
He has been characterised as one of the greatest art thieves among the Nazis, and possibly ever.