This Investigation was carried out to study the influence of differ­ent temperature degrees, short ultra-violet and direct sunlight on the rate of decomposition of dazinon and pirimiphosmethyl insecticides, which are widely used in Egypt to protect vegetable crops from econom­ic pest. The results indicated that the increase 01 temperature degrees means an increase in insecticide residue loss. The percentage loss of die­zincn and pirimiphos-methyl insecticides was reached 39.03% and 11.58% at 20 °C; 99.97% and 58.48% at 30 °C; 99.99% and 97.53% at 40 and 100%. and 99.90% at 50 °C, respectively after 192 hours of the lime exposure . On the other hand, the half life values of the two in­secticides were >192 and >192 hours at 20 'C; 70.79 and 158.76 hours at 30 C :17.46 and 57.76 hours at 40 °C and 7.78 and 31.94 hours at 50 V. respectively. In general, increasing temperature degrees and pro­longation of exposure increase the percentage loss of insecticide. Pirimi­phos-methyl had the highest thermal decomposition during the periods of experiment. Diazinon was less stable than pirimiphos-methyl when exposed to UV- rays after three hours from application. The percentage loss of dia­zinon and pidmiphos-methyl insecticides after 24 hours was 61.61 % and 80.53 %, respectively. The half-life values of the two insecticides were 13.59 and 8.77 hours, respectively. The rate of degradation of the two tested insecticides varied according to their chemical structure, time of exposure and the wave length of UV-rays used. Pirimiphos­methyl was the most affected by UV irradiation compared with diazinon Insecticide. The tested insecticides greatly deteriorated when exposed to di-red sunlight. The percentage loss of diazinon and pirimiphos-methyl were 100% after 48 hours from exposure. The hall-life values of the diazinon and pirimiphos-methyl were 1.02 and 0.60 hours, respectively. The active ingredient of the two in­secticides greatly deteriorated when exposed to direct sunlight. Sunlight