In this study, it was aimed to determine the chemical composition of the pufferfish (Lagocephalus sceleratus) caught from Mersin Bay in the Northeastern Mediterranean Sea. For this purpose, the proximate composition, fatty acid profile, mineral and heavy metal levels were investigated. Pufferfish samples were caught using trawl fishing technique over four seasons between December 2012 and October 2013. As a result of the study, the average protein, lipid, water and total mineral substance (TMS) levels for female individuals were determined to be 20.44%, 0.65%, 76.98% and 1.43% respectively; while for male individuals these were determined to be 20.58%, 0.84%, 76.68% and 1.40%. In the fatty acid composition of L. sceleratus; total saturated fatty acids (SFA) level was determined to be between 24.78% and 29.75%, total monounsaturated fatty acid (MUFA) level was 15.41% to 23.20%, total polyunsaturated fatty acid (PUFA) level was 39.90% to 45.70%. Macro, trace element and toxic heavy metal levels in pufferfish muscle tissue were determined using ICP-MS. The relationship between the amounts of macro and trace elements in L. sceleratus was determined to be K>P>Na>Mg>Ca and Zn>Se>Cu>Ni>Mo>Co for both sexes. In the muscle tissues of pufferfish, Cd levels were found to be over limit levels.