This study was conducted to determine the suitable concentration of chitosan to flocculate Chaetoceros algae and to feed juvenile of blood cockle, Anadara granosa. There were 2 experiments in this study, each experiment included 4 treatments and triplicates per each. In experiment 1, Chaetoceros algae were flocculated by difference concentrations of chitosan at 10, 40, 70, and 100 mg/L. In experiment 2, blood cockle juveniles were fed flocculated algae with three concentrations of chitosan at 40, 70, 100 mg/L and centrifugal Chaetoceros was used as control diet in 60 days. Results from experiment 1 showed that Chaetoceros algae were flocculated with chitosan from 40-100mg/L resulting in similar flocculation efficiency (91-92%) after 7hours. Concentrations of chitosan increasead from 10-100 mg/L resulted in total bacteria density decreased (P0.05). In experiment 2, the highest growth rate of blood cockles was observed in chitosan flocculated algae at 40 mg/L after 60 days of culture and the results were similar to those from centrifugal algae diet. Results from this study indicated that Chaetoceros algae were flocculated by chitosan at 40 mg/L being suitable for rearing blood cockle juveniles.