Oysters, mussels and limpets were collected from thirteen sites along the intertidal rocky shoreline of Beppu Bay and arsenic contents in the specimens were determined. On the other hand, oysters, chitons and limpets were collected along the rocky shoreline and also short-necked clams from sand bed of a site in Miyazaki Prefecture, and the contents were also determined. Potential arsenic pollution in Beppu Bay was discussed on the basis of the concentration differences between the specimens collected in common from the two areas. In the oysters and the limpets collected in common from the two areas, the arsenic contents were consistently higher in those from Beppu Bay than those from Miyazaki Pref. In Beppu Bay, the contents in oysters were rather higher in those from the two sites in Saganoseki Inlet than in those from all of the other sampling sites, and in mussels a similar phenomenon was noticed. In a single site from which the three specimens were collected in common, the order of arsenic content was as follows: limpets>oysters>mussels. Between oysters and limpets collected from all of the sampling sites in Beppu Bay, the contents were consistently higher in the latter than in the former. On the other hand, in the specimens collected from the shoreline of Miyazaki Pref., the contents in oysters were almost equal to those in limpets. The arsenic levels of chitons were nearly equivalent to those in limpets and oysters. The relatively high level of arsenic equivalent to that of the oysters from Beppu Bay was found in short-necked clams from a site in Miyazaki Pref. From these contexts, it was demonstrated that the high arsenic accumulation existed in the littoral forms in Beppu Bay, in which much grossly polluted specimens were found locally. Such high arsenic accumulation could be explained by biomagnification through arsenic level elevated to sea water.