Julius Dettmann (January 23, 1894 – July 31, 1945) was a German officer of the Sicherheitsdienst (SD) of the Schutzstaffel (SS).
Dettman belonged to the SS with the card number 414,783, and to the Nazi Party with card number 722,240, member of Section IVB4 of the Gestapo. He was stationed in Amsterdam during the German occupation of the Netherlands. He was promoted to SS Obersturmführer (Lieutenant) on November 9, 1942. On August 4, 1944, he received a phone call reporting that there were Jews hidden on the premises at 263 Prinsengracht in Amsterdam. The people in question were Anne Frank, her parents, sister, and four others. He immediately dispatched a commission led by SD Oberscharfuhrer (Staff Sargent) Karl Silberbauer, telling Silberbauer that the call had come from "a reliable source". Silberbauer and his contingent of NSB plain-clothes officers raided the building and arrested the eight in hiding who, after questioning at SD headquarters, were deported to the Westerbork transit camp and from there to the Auschwitz concentration camp.