Apoptosis in leaves and protoplasts from homokaryon maize Mo17-C and Mo17-N treated by Helminthosporium maydis race C （HMC） toxin were detected by DNA ladder and hoechest 33258 respectively. The DNA ladder result indicates that DNA ladder appeared in both Mo17-C and Mo17-N, and the obvious DNA ladder in Mo17-C appeared after 12 h induction when the concentration of HMC reached 250 μg/mL, but appeared in Mo17-N when the concentration reached 300 μg/mL. Protoplasts of both Mo17-C and Mo17-N revealed apoptotic features such as apoptotic bodies, ring chromatin or chromatin margination. The apoptosis rate of Mo17-C maize protoplasts were significantly higher than that of Mo17-N in the same treatment, and it increased with the increase of treatment time and concentration. So, it is concluded that Mo17-C was more sensitive than Mo17-N.