In this study, newly fertilized eggs of Gobiocypris rarus were used as test material and exposed to graded doses of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD) (0.002, 0.005, 0.01, 0.03, 0.05, 1.0, 5.0, 10.0, 50.0, 100.0pg/ml) from the first day of embryonic development. The toxicity of TCDD and its effects on the development at early life stage were observed and 7-ethoxyresorufin-O-deethylase (EROD) activities in different development stages of Gobiocypris rarus were measured. The results showed that at early life stage of Gobiocypris rarus, the EROD activities in eggs exposed to TCDD dose groups (1.0 - 100. 0ppt) were significantly induced and increased with TCDD concentrations; while no difference was found between low TCDD dose groups (<0.1ppt) and the control group during early life stage. But a good relationship between the EROD activity and TCDD concentration was observed during long time development stages, this result also revealed the bioaccumulation regularity of TCDD in fish.