The present study was carried out on soil cultivated with cotton variety Giza 70 during the season of 2011 to determine the side effects of certain pesticides i.e.; chlorpyrifos, profenofos, cypermethrin and alphacypermethrin which were used  against the cotton bollworms on soil enzymes of  urease and dehydrogenase. Three sprays for each insecticide were done and the spraying is carried two weeks after the previous spray.  The average of urease activity for the three sprays were expressed as unconverted urea to NH4-N (%).The results showed high enzyme activity in all treatments, while, the mean enzyme activity was significantly decreased after treatment with profenofos.   For the average of enzyme dehydrogenase activity for the three sprays that expressed part per million (ppm) Formazan were determined. The results showed higher enzyme activity after application with chlorpyrifos, while, the activity was significantly decreased after application with Cypermthrin and profenofos, but, alphacypermethrin had mild effect on the enzyme. It concluded that profenofos reduced urease and dehydrogenase activities. While cypermthrin decreased dehydrogenase activity . On the other hand, chlorpyrifos increased urease and dehydrogenase activities.