Abstract: The effects of 4 pesticides (thiophanate-methyl,mancozeb,fenvalerate and abamectin)on soil phosphatase activity and respiration of soil microorganisms were investigated in this study.Safety levels of the four pesticides were also evaluated.Results show an irrecoverable inhibition of phosphatase activity in soils treated with thiophanate-methyl or mancozeb.Phosphatase activity of fenvalerate or abamectin treated soils are initially inhibited,but then reactivated after 7 days and hitting peak values 35 days after treatment.Reactivation gets stronger with higher concentration of fenvalerate and lower concentration of abamectin.Soil respiration is slightly stimulated during the initial period,inhibited after 5 days,and then recovers to control levels after 12 days.Safety evaluation shows that the four pesticides are slightly,but not practically, harmful to soil microorganisms due to their inherent toxicity.