Abstract: Phagocytosis, the cellular defensing reactions of Eriocheir sinensis, was studied in vitro using Bacillus cereus and formalinized mouse erythrocytes as test particles. The results showed that 100.0 mgmL-1 L-cysteine van HARREVALD's solution could anticoagulate hemolymph of E.sinensis. And phagocytosis was studied using a monolayer culture system which maintained cell viability at (92.50.9)% for 1 hour at 20℃. Many of spread cells were phagocytic cells, which had pseudopodia and could phagocyte B.cereus in vitro. Uptake of the Gram-positive bacteria, B.cereus, was found to be (5.11.4)%. The formalinized mouse erythrocyte was not phagocytosed at all. Serum incubation did not increase the percentage of uptake of any of the test particles with the haemocytes.