Walter Rethel (1892–1977) was a German aircraft designer.
Working for the Dutch company Fokker in the years after World War I, he designed aircraft such as the amphibious Fokker B.I and the Fokker F.VII airliner. In the 1920s he worked for Arado Flugzeugwerke in Germany, before moving to Messerschmitt, where he was chief engineer on the legendary Bf 109.