The residues of difenoconazole fungicide (Score 25% EC) on and in tomato fruits and under environmental conditions were determined by high performance liquid chromatography (HPLC) equipped with UV variable wavelength detector. The initial deposit of this compound was 6.72 ppm one hour after tomato treatment. This amount decreased gradually to 5.86, 4.83, 2.25, 1.58 and 0.20 ppm 1,3,5,7 and 14 days from application respectively. These figures show 12.8, 28.13, 66.52, 76.49 and 97.02% loss in the same intervals, respectively. The half life value of difenoconazole on tomato fruits was 79 hours (about 3 days) under the environmental conditions of the experiment. As the maximum residue limit (MRL) of difenoconazole on tomato fruits was 1 ppm. Hence, the preharvest interval (safety period of consumption) is 8 days post treatment. The washing process by tap water dropped the initial deposit of difenoconazole residues from tomato fruits to 1.79 ppm recording 73.36% loss. Temperatures, UV-rays and direct sunlight affected the stability of difenoconazole when exposed on glass surface. Therefore, the time taken for 50% degradation (T1/2) of difenocoazole were 118, 34, 12 and 11 hours at 30, 35, 45 and 50 ⁰C, respectively. Hence, the difenoconazole residue was more stable under exposure to ultraviolet rays than exposure to direct sunlight.