With the aim of exploring immunological difference between black and yellow shell-coloured Pomacea canaliculata,an acute toxicity test of niclosamide was carried out,and their mortality of niclosamide,the cytochemistry characterization and neutral red retention time(NRRT)of hemocytes were investigated in two kind of snails.The results showed the LC₅₀ value of niclosamide for the black-shell snails were 0.77 mg/L and 0.46 mg/L at 24 h and 48 h,and they were higher than the yellow-shell ones.Cytochemical stains(alkaline phosphatase,acid phosphatase,peroxidase,sudan black B,periodic acid schiff,neutral red)showed that most of positive hemocytes were located in the cytoplasm,and the granulocytes were strongly stained.The percentage of positive hemocytes to ACP,AKP,POX of black snails was higher than that in the yellow ones,especially the value of AKP and POX(P<0.01).The intensity of PAS staining in the black snails was stronger than the yellow ones.However,there was no significant difference between NRD and SBB staining.NRRT indicated that the time of neutral red retention in hemocytes of black snails was 9.15 min,which was 1.8 times longer than the yellow ones.This implied that hemocytes of the black snails have higher lysosomal stability.Therefore,the susceptibility of niclosamide,AKP,POX,glycogen and lysosomal stability could affect the immunological function of P.canaliculata.