The toxicity of six pesticides at 800, 600, 400 and 200 ppm doses to the egg, nymphs and adult of Tetranychus bioculatus was investigated by bioassay using mashkalai leaf as a substratum. The eggs of mite remained unhatched at all dosage levels of six pesticides 72 hours after treatment. The ovicidal action of these compounds may be associated with the dose lower than 200 ppm. The acaricides, folimat and zolone and the insecticide, vapona killed 73-79 % and 46-48 % nymphs at highest dose 800 ppm and lowest dose 200 ppm respectively. Gusathion, malathion and diazinon produced nymphal mortality below those ranges. The LD50 values indicated that folimat ·was the most toxic followed by vapona and zolone; malathion and gusathion were less toxic and diazinon was the least toxic to the mite nymphs. The adult mites had mortality almost in the same pesticide order as nymphs but significantly with lower proportion. Of the developmental stages of T. bioculatus, eggs appeared to be more susceptible than nymphs which were more susceptible than the adults.