The purpose of this study was to investigate the hypothesis weather the combination of lead acetate and deltamethrin can enhance avian toxic effects produced by lead exposure only. Overall, 48 Japanese quails, Coturnix coturnix Japonica (15 day old) were randomly divided into 4 experimental groups of 12 birds each and sex ratio of 1:1. Experimental groups consisted of control Japanese quails, birds exposed to a single dose of lead acetate and lead acetate combined with sub-lethal doses of deltamethrin (0.25 and 0.50 mg. kg^-1 diet) for 21 days. We studied the effects of a single dose of lead acetate, combined with deltamethrin, on survival and blood biochemical parameters of Japanese quails. The results revealed a significant increase in plasma AST and ALT activities, glucose, uric acid and creatinine levels after feeding quails with contaminated diet (P <0.05). There was a significant increase in CPK and LDH activities and triglyceride levels in the blood of quails fed diets contaminated with a combination of lead acetate and deltamethrin (P <0.05). The decrease in AChE and ALP activities, total protein, and globulin was observed in plasma of quails fed contaminated diets. There were no significant changes in albumin levels. Although oral administration of lead acetate combined with 0.25 mg deltamethrin caused a significant increase in cholesterol levels, no significant differences were observed in triglyceride levels in other treatments. The synergic effects of deltamethrin on the alterations in the blood biochemical parameters of quails exposed to lead highly depend on the concentrations of this pesticide in feedstuffs.