Abstract: An experiment was conducted to explore the effect of ingestion and digestion of pearl oyster (Pinctada fucata) on microalgae of different types and concentrations from aspects of particle size, surface structure, biochemical composition and feed concentration. The mixture of Chaetoceros muelleri and Dicrateria zhanjiangensis with similar size and the mixture of Platymonas subcordiformis and Marine chlorella with different sizes were fed to pearl oysters. Cells count was detected in the remaining mixture microalgae. C.muelleri, D.zhanjiangensis, P.subcordiformis and M.chlorella of different concentrations were fed to pearl oyster to compare the digestion of microalgae in feces. The results show that selective feeding was not significantly different (P>0.05) between microalge with similar size, while the ingestion rate raised with increasing size (P < 0.05). The digestion rate decreased with increase of diet concentration.