The present investigation was carried out to determine the residues of the insecticide fenobucarb on and in tomato fruits with referring to the effect of washing process in eliminating residues from fruit surface. Photo and thermal degradation with some environmental factors namely UV-rays, direct sunlight and different temperature degrees was performed. Recovery rate of fenobucarb residues was carried out on tomato fruits at the level of 1ppm and the rate of recovery average was 95.5%. Tomatoes were planted and treated with fenobucarb at the recommended rate 312cm3 per feddan under the normal Egyptian field conditions The initial deposit of fenobucarb on and in tomato fruits was 8.07ppm and the obtained residue half-life value (t1/2) was 24 hours. Washing process removed 67.70% of the initial deposit remained on tomato fruits. The calculated half-life periods were 4 and 3.8 hours when exposed to UV-rays and sunlight, respectively. The results showed that fenobucarb was degraded more rapidly at high temperature degrees than the lower degrees. The half-life periods were 37, 24, 17 and 5 hours at 30, 35, 45 and 50ºC, respectively.