Germinating seeds of three rice varieties （a high quality Huaxianzhan, a hybrid Yueyouqingzhan and a comman Suilingzhan） were treated with acetochlor at three concentrations. The growth of rice seedling was differently inhibited. Huaxianzhan was the most sensitive variety, Suilingzhan the most resistant and Yueyouqingzhan the inter mediate. During 2 ~ 10 days after germination, acetochlor had no distinct inhibition to amylase-isoenzyme and the activity of a-amylase in all the three rice varieties. However, the β-amylase in sensitive variety was heavily inhibited on the 6th day after germination. According to this fact, the study concluded that one important physiolgical cause for rice's sensitivity to acetochlor might be the inhibition of 3-amylase in rice by the herbicide.
