The aim of the present study was to study the effects of tulathromycin on the fertility of male rats indicated by evaluation of semen picture, measuring the testosterone level and pathologic changes of testes. The later included routine histopathologic examination as well as morphometric analyses of seminefrous tubules and epididymal duct diameters. Thirty apparently healthy adult Albino male rats (average weight 160-200 g) were allocated into 3 equal groups (n=10). Rats of the first group was kept as control and injected with 0.1 ml normal saline subcutaneously once weekly for three successive weeks. The animals of the second group were subcutaneously injected with tulathromycin in a dose of 2.5 mg/kg B.wt twice with 15 days interval, and the third group were subcutaneously injected with tulathromycin (2.5mg/kg b.wt) for three successive weeks. Rats were sacrificed at 65 days of treatment and testes and epididymes were removed, weighted and histopathologically examined. Results revealed that tulathromycin administration significantly (p<0.0001) decreased the weight of testes and epididymes and adversely affect the semen quality (decreased sperm cell count and motility and increased abnormalities). Testesterone level was significantly (p<0.0001) deceased. Histopathological examination revealed that, degenerative changes of spermatogenic cells and reduction in numbers of spermatozoa in the central lumen of seminiferous and epidydimal tubules were found in groups treated with tulathromycin. Statistically, a significant differences between injected and control groups were detected using morphometric analyses of seminefrous tubules and epidydimal ducts diameter, indicating that tulathromycin pose a negative effect on the histology of the testes. It could be concluded that fertility of rats was adversely affected by repeated injection of tulathromycin in a therapeutic dose of (2.5 mg/kg b.wt).