Abstract: Objective:To evaluate the effect of carboxylated single-walled carbon nanotubes (c-SWNTs) on the development and morphology of zebrafish embryos in the water environment.Methods:According to the national standard GB/T21807-2008, healthy zebrafish embryos were exposed to c-SWNTs of different concentrations(40, 80 and 160 mg/L) in aqueous dispersions at 6 h post fertilization (6 hpf).And the hatching rate, malformation rate and mortality rate of the embryos at 24 hpf and 96hpf were observed and analysed.The effect of 80 mg/L c-SWNTs on the morphology and embryonic ultrastructure of the zebrafish embryos at 24 hpf was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively.Results:Compared with the control group, there was no significant difference in the hatching rate, malformation rate and mortality rate of the embryos among exposed groups at 24 and 96 hpf, except for the hatching rate of embryos with a significant decrease in the 40 mg/L group at 96 hpf(P< 0.05).SEM results showed that c-SWNTs aggregated on the outer surface of the embryonic chorionic membrane and had difficulty penetrating the chorionic membrane.TEM results showed that no significant c-SWNTs were observed in the internal ultrastructure of the embryos.Conclusion:The carboxylated single-walled carbon nanotubes in the water environment mainly aggregate on the outer surface of the embryonic chorion and will affect the hatching time of some embryos, but have no significant effect on the development of zebrafish.