Pond snail Bellamya chinensis is one of the dominant aquatic snails in wetland ecosystem especially rice field in Japan. They have seemed to ingest algae and organic matter in sediment as deposit feeder. However some researchers showed they have a potential to ingest suspended matter by filter feeding. Moreover feeding on attached algae on their shell has been observed in the field. Contribution of each potential food source, namely sediment, suspended matter and attached algae on their shell on B. chinensis is unknown. In this study we conducted field survey in a rice field in Miyagi prefecture, Japan to clarify contribution of their food sources by using stable isotope ratio of essential fatty acids, 18:3n3 in both snail and potential food sources. The stable isotope ratio of 18:3n3 in snail was -32.0‰. The stable isotope ratio of 18:3n3 in sediment, suspended matter and attached algae on their shell was -35.2‰, -41.5 and -34.2‰ respectively. While the stable isotope ratio of essential fatty acids of snail was heavier than those of potential food sources, sediment and attached algae on their shell showed relatively closed value of snail. It indicated these potential food sources were mainly assimilated by snail. In contrast contribution of suspended matter seemed to be relatively low.