The effects of insecticides on biochemical processes in soil were studied by determining the effects of the chemical structure of each insecticides on enzyme activities, pesticide residue and total number of bacteria revealed when soil treated with urea. was incubated at 28±1° for 56 days. The inhibition effects of insectides on enzyme activities in soil decreased in the order: dithiophosphoric acid $gt; thiophosphoric acid $gt; phosphoric acid $gt; carbamate insecticides fur urease and phosphatase, thiophosphoric acid $gt; dithiophosphoric acid $gt; phosphoric acid $gt; carbamate insecticides for L-glutaminase and protease. The inhibition effects of organophophorus insecticides on enzyme: activities in soil were maintained longer than those of carbamate insecticides. Carbamate insecticides increased the activities of protease and L-glutaminase at 56 days. When insecticides were treated in soil together with urea, the degradation of insecticides was accelerated. By treatment of insecticides, the total number of bacteria was decreased at the early stage of treatment but thereafter increased according to phosphoric acid and carbamate insecticides.