This paper presents the investigation results of methylmercury and total mercury in gastropod and bivalve species collected from eight coastal sites along the Chinese Bohai Sea. The total mercury was directly determined by atomic fluorescence spectrometry (AFS), while the methylmercury was measured by a laboratory established high performance liquid chromatography-atomic fluorescence spectrometry system (HPLC-AFS). Certified reference material DORM-2 (Dogfish muscle) was used to validate the two methods and the obtained results proved to be in good agreement with the certified values. It was demonstrated that the mercury contamination was commonly existed in all selected mollusks, with methylmercury and total mercury concentration in the range of 4.8-168.4 and 6.7-453.0 ng Hg g(-)(1), respectively. Mollusks from HuLuDao were the most mercury contaminated, and those from PengLai took the second place. The species-dependent bioaccumulation capacity was observed in this study. Gastropods showed more capacity to bioaccumulate mercury than bivalves, and mercury contents in two kinds of gastropods (Rapana venosa and Neverita didyma) presented some uplifted trends with the dimensions increasing of the gastropods. Rapana venosa was found to be a potential biomarker to monitor mercury pollution in oceans. Evaluations were also made concerning about the ratio of methylmercury to total mercury.