The purpose of this study was to investigate the developmental toxicity of copper sulfate (CuSO4) and the inhibitory effect of rosmarinic acid (RA) on the zebrafish (Danio rerio) embryos. The embryos (1 hour post fertilization, 1 hpf) were exposed to different concentrations of CuSO4 solution and CuSO4 solution containing different concentrations of RA, respectively. Control group was exposed to E3 medium. The mortality, malformation and hatching of embryos were observed under stereo microscope. The lethal rate, malformity rate and hatching rate were calculated and analysed. The embryonic reactive oxygen species (ROS) was detected using the fluorescent probe of DCFH-DA under RA defense. The experimental data were statistically analyzed with variance analysis. The results showed that the exposure to the CuSO4 solution caused serious lethal effect (Fig. 1a) and teratogentic effect (Fig. 1b, 2), decreased the hatching rate of embryos (Fig. 3) in a concentration-dependent manner. The linear regression equation between concentration of CuSO4 and mortality of zebrafish embryos at 96 hpf was Y = 5.59X + 7.1533, Y and X referred to lethal rate (%) and concentration of CuSO4 (μmol/L), respectively. The corresponding half lethal concentration (LC50) of CuSO4 on zebrafish embryos was 7.7 μmol/L. The linear regression equation between concentration of CuSO4 and deformity rate of zebrafish embryos at 96 hpf was Y = 24.213X + 3.5443, Y and X referred to lethal rate (%) and concentration of CuSO4 (μmol/L), respectively, and the half effective concentration (EC50) resulted in the malformation was 1.9 μmol/L. At 96 hpf, RA decreased lethal effect and increased hatching of zebrafish embryos induced by 8 μmol/L CuSO4 (Fig. 4). RA decreased malformation effect of zebrafish embryos induced by 1.6 μmol/L (Fig. 5). CuSO4 and RA inhibited ROS level induced by CuSO4 in zebrafish embryos (Fig. 6). The results indicate that CuSO4 has serious toxic effect on the development of zebrafish embryos, which may be associated with increased ROS level and caused oxidative stress. RA inhibits developmental toxicity of CuSO4 by reducing oxidative stress.