Objective To establish a rapid and accurate determination method for detecting thallium in fish.Methods Thallium was determined by optimal microwave-digestion-ICP-MS.Results The linear range of this method was 0.5-10 μg/L(r=0.9999),detection limit was 0.2 μg/kg,relative standard deviation(RSD) was under 10%,recovery rate was 80%-99%.Conclusion The method of microwave-digestion-ICP-MS was sensitive,accurate,convenient and rapid for determination of thallium.