Abstract: Carassius auratus were chosen as the experimental materials to study the dynamic effects of 1 mg/L 2-nitro-4′-hydroxydiphenylamine on the induction of HSP70 in the gills of the fish exposed in different periods. The SDS-PAGE and Western Blotting techniques were used to detect the expression level of HSP70 in the fish gills. The feasibility of applying HSP70 in fish gills as environmental biomarker of 2-nitro-4′-hydroxydiphenylamine was also explored. As shown from the results, 2-nitro-4′-hydroxydiphenylamine can induce the HSP70 significantly (P<0.05). Comparing with the control group, the HSP70 in the fish gills began to express significantly after 2 days exposure and the expression level of HSP70 was enhanced after 4 days. The expression level began to decrease after 7 days. But maybe for the high toxicity of the long exposure of 2-nitro-4′-hydroxydiphenylamine, the tissue damage and pathologic change of fish gills were caused, and the expression level of HSP70 decreased significantly afterwards, far below that of the control group (P<0.05). Therefore the HSP70 in fish gills is not appropriate to be environmental biomarker of 2-nitro-4′-hydroxydiphenylamine in the aquatic ecosystem.