This research reports the first data on mercury levels found in Giant otters (Pteronura brasiliensis) from South America. Mercury concentrations were analyzed from different organs/tissues of two animals found dead floating on the water of the Rio Negro in the Pantanal, Brazil. The mean mercury concentration ranged from 2.94 to 3.68 microg/g in hair, from 1.52 to 4.3 microg/g in liver, and from 1.11 to 4.59 microg/g in kidney and was 0.17 microg/g in muscle samples. In comparison with other research, there is no evidence of contamination in these animals and mercury concentrations in tissues appeared to be at levels below those associated with toxicity.