Apoptosis in protoplasts from homokaryon maize B37(CB37,NB37) and Mo17 (CMo17,NMo17) inbred lines treated by HMC-toxin were studied. Homokaryon maize B37 and Mo17 inbred lines were tested and the protoplasts may be stained by AO and EB. The protoplasts were divided into 4 groups. 3 groups were treated by 0,50,100,150 μg/mL of HMC-toxin as the experimental groups,and the induced time were 1,3,6 h to study the feature of apoptotic and the rate of apoptosis. The apoptotic features such as apoptotic bodies,chromatin margination or ring chromatin were found after the treatment. When treated by HMC-toxin with different concentrations,the apoptosis rates of CB37,NB37,CMo17 and NMo17 maize protoplasts were 10.80%, 4.90%, 21.00%, and 8.83%. Accordint to the above study,a conclusion can be reached as follows: apoptosis in protoplasts from homokaryon maize B37 were the same as that of Mo17; CB37 and CMo17 were more sensitive to HMC-toxin than NB37 and NMo17, respectively; when treated by the same concentration of HMC-toxin,the apoptosis rates of CB37 and CMo17 maize protoplasts were significantly higher than NB37 and NMo17 respectively; the rates of apoptosis were significantly different between C and N,and the former was significantly higher than the latter. In addition,the apoptosis rate increased when the treatment time and the concentration increased.