Supercritical carbon dioxide extraction was investigated as a method for removing lipids and bad flavor from tuna viscera. To find the optimum conditions, different experimental variables, such as pressure, temperature, flow rate of solvent and sample size, were evaluated for the effective removal of lipids and the undesirable smell. Ethanol was used as the entrainer, with a $3\%$ by vol $CO_2$ flow rate. By increasing the pressure at constant temperature, the efficiency of the lipid removal was improved and the protein was concentrated without denaturalization. The main fatty acids extracted from the tuna viscera were palmitic acid (16:0), heptadecanoic acid (17:1), oleic acid (18:1) and docosahexaenoic acid (22:6). The major amino acids in the tuna viscera treated by supercritical carbon dioxide were glutamic acid, leucine and lysine, and the free amino acids were L-proline, taurine and L-$alpha$-aminoadipic acid.