Abstract: The effects of methamidophos of five different concentrations on the activities of phosphatase and dehydrogenase in soil have been reported. The research results showed that 2～24 days after the application of methamidophos, the activities of all the three sorts of phosphatase and dehydrogenase were inhibited in varying degrees,and the higher the inethamidophos concentration the greater and longer the influence. But the influence had been continuously reducing with time, finally, the enzyme activitics were even slightly stimulated. The influence of methamidophos on the activity of acidic phosphatse was greater than that on the activities of neutral and alkaline phosphatase. The effect of methamidophos on the relationship between microbial growth and enzyme activities has also been briefly discussed.