BACKGROUND: Fish and fish products are consumed in many countries as a considerable source of nutrients. The heavy metals contents are known to increase drastically in the marine environment. OBJECTIVES: The present study investigated the contents of cadmium (Cd), lead (Pb), and mercury (Hg) in four com-mercially valuable fish species of the Caspian Sea (Rutilus frisii kutum) and Persian Gulf (Parastromateus niger, Pomadasys kaakan, and Scomberomorus commerson). METHODS: A total of 200 samples were collected randomly from fresh fish. A microwave-assisted digestion method was conducted to prepare fish samples and atomic absorption spectroscopy was used for determining heavy metals. RESULTS: The ranges obtained for heavy metals were 0.013-0.038, 0.127-0.352, and 0.007-0.067 mg/kg for Cd, Pb, and Hg, respectively. No fish species overpassed the standard concentrations of metals set by the national or international standards, except for the mean level of Pb in Parastromateus niger. CONCLUSIONS: Results of the present study indicated that Pb, Cd, and Hg were found in Iranian fish species exclu-sively in trace levels except for the Pb content of the black pomfret of the Persian Gulf. The concentrations of these elements did not exceed the legal limits of the European Commission or the Institute of Standards and Industrial Research of Iran.