Abstract: The purpose of this study was to evaluate the effect of pesticides on blood indices of subjects which are exposed to organophosphate toxins. This research was a cohort study which was carried out during 2005 on the employee of a pesticide factory in Golestan province (North of Iran). In this study the sampling from 63 subjects was carried out for two sessions in days 1 and 90. CBC and hematologic indices performed by cell counter instrument. The mean of MCV in phase 1 was 82.8±7.1 fl and in second phase the MCV was 80.3±6.7 fl. This drop in MCV statistically was meaningful (paired t-test, mean = 2.5, 95% CI=2.0-2.9, p<0.001). Erythrocyte number, hemoglobin, HCT and MCHC increase in second phase compared to first phase statistically was meaningful. There was not any significant relation between the place of work and variation of red blood cell indices. In regard to the changes in hematologic indices in workers of pesticide factory in a three months period, it seems logical to set up a program to have a routine check on the hematologic indices in working personal engaging in such occupations.