The present work was carried out to study the persistence of Fenarimol (Rubigan 12%EC), Triflumizole (Trifimine 15%EC) and Penconazole (Topas 10%EC) under certain environmental factors. The stability of active ingredients under accelerated storage through 54°C for 14-60 days, and through different temperatures (25°, 35°C and 45°C) for 1-192 hours, under direct ultraviolet and sunlight rays, were also considered. Generally the chemical residues of the studied pesticides were estimated by HPLC. The obtained results proved that : Fenarimol was more stable than other pesticides after storage for different period at 54°C and effect different temperature (25°, 35°C and 45°C). On the other hand, under direct ultraviolet and direct sunlight rays. The data presented showed that the rate of degradation of Penconazole was more rapid than Fenariol and Triflumizole in their formulations, while Triflumizole was more stable. Finally the different physical properties for unstored and stored tested pesticides are all within the allowed limits according to WHO and FAO.