Monocrotophos was administered orally to adult male albino mice at dose level of 3.0 mg/kgbody weight/day/mice for 50 days. The treatment has found to affect spermatogenesis as well asthe endocrine functions of the testis as indicated by gravimetric, histopathological andbiochemical changes. The treatment has caused degenerative changes in the seminiferous tubulesand Leydig cells of the testis and regression of the epididymis, seminal vesicle, vas deferens,prostate, Cowper’s gland and levator ani. Similarly, cauda epididymal sperm count and spermmotility have shown significant reduction. There was a significant reduction in the protein,glycogen, sialic acid, acid and alkaline phosphatase and increase in cholesterol in the testis ofmonocrotophos treated mice compared with the control. The causative factors for these changesdue to monocrotophos administration were discussed.