A rapid analysis of methylmercury (MetHg) in fish samples is reported by using stannous chloride reduction and direct sampling electrothermal vaporization atomic absorption spectrometry (ETV-AAS). After the simple reduction reaction using 10% SnCl2 (w:v), Hg2+ was changed to volatile Hg0 and vaporized from the analyte extraction solution. Then, the residual Hg species was determined with the direct sampling Hg analyzer without requiring chromatographic separation. Since the dominating organic Hg in fish tissues is mostly MetHg (methylmercury), the measured alkyl Hg residue can therefore be considered to be MetHg+ for rapid screening. The LOD (detection limit) of the proposed method reached 0.6 μg/kg of MetHg with 0.4% - 6.3% RSD (relative standard deviation). No significant difference (P > 0.05) was found between the proposed method and the liquid chromatographic atomic fluorescence spectrometry (LC-AFS) method or certified values of reference materials, which proves the accuracy of the MetHg analysis in real marine and freshwater fish samples. The total testing time for one aliquot, including instrumental analysis (~3 min) and sample preparation, can be performed within 100 min. Considering the possible EtHg (ethylmercury) existence in most fish samples, it is suggested that this proposed method be used for future rapid screening analysis, which no doubt also offers considerable applicable potential for fast mercury speciation analysis to protect food safety.