Guilherme Dias Massê Basseto (born 12 March 1997) is a Brazilian swimmer. He was at the 2017 Summer Universiade in Taipei, Taiwan. He competed in the men's 50 metre backstroke and in the men's 100 metre backstroke events at the 2018 FINA World Swimming Championships (25 m), in Hangzhou, China, reaching the semifinals of both (finished 13th in both). On 25 April 2021, while swimming the 4x100m mixed medley relay at the Brazilian Olympic Selection Trials, he broke the South American record with a time of 3:45.51, along with Felipe Lima, Giovanna Diamante and Larissa Oliveira.