Nelson Dieppa-Gerena (born February 25, 1971) is a Puerto Rican professional boxer. As an amateur, he represented Puerto Rico in international events including the 1991 World Amateur Boxing Championships, 1991 Pan American Games and the 1992 Summer Olympics. Dieppa debuted as a professional on February 13, 1993, when he defeated Carlos Figueroa. His first world championship fight took place on July 3, 2000, when he lost to Will Grigsby for the World Boxing Organization's light flyweight championship. Following this fight Grigsby tested positive for illegal drugs and the title was declared vacant. Following this fight the title was won by Masibulele Makepula but was stripped again. He won the vacant title on April 14, 2001, in a fight against Andy Tabanas. Dieppa defended the title successfully five times before losing it to Hugo Cázares on April 30, 2005.