Marcela Valeria Britos (born February 26, 1985 in Maldonado) is a Uruguayan track and field athlete, who specialized in middle distance running. She represented Uruguay at the 2008 Summer Olympics in Beijing, and competed in the women's 800 metres. She ran in the third heat of the event, against six other athletes, including Kenya's Pamela Jelimo, who eventually became an Olympic champion in the final. Britos finished the race in last place, with a time of 2:08.98, but was upgraded to sixth position in this heat, when Croatia's Vanja Perišić had been disqualified for failing the doping test.