Protective effects of N-acetylcysteine (NAC) on homocysteine (Hcy)-induced injury have been reported in vitro. However, it is not known whether NAC has a similar effect in Hcy-induced injury during embryonic development. In this study, we tested the hypothesis that exogenous NAC can attenuate Hcy-induced injury in chick embryos. Hcy-induced apoptosis and reduced embryo viability were effectively attenuated by application of exogenous NAC. NAC could also rescue Hcy-induced inhibition of extra-embryonic vascular development. 2',7'-Dichlorofluorescein diacetate, an indicator of reactive oxygen species, was detected in H9C2 cells after treatment with Hcy. The results of this study provide the first evidence that NAC can protect against the adverse effect of Hcy during chick embryo development, and suggest that these effects are at least partly mediated by oxidative stress.