This experiment was conducted to evaluate the impact of dietary L-arginine supplementation on some epididymal spermatozoa characteristics, differential White blood cells count, some reproductive organs'metrics. Fifteen adult Ossimi rams averaging 44.9± 0.57 kg were utilized, divided into three comparable groups (5 rams each) , were fed a basal ration supplemented with L- arginine at concentration of 0.0 (G1) or 0.5(G2)  or 1.0%(G3) of body weight/day for two months. At the end of the study rams were slaughtered for conducting biometric studies on tests and epididymis and testicular Immunohistochemical NOS analysis. Epididymis Semen was collected and evaluated for  motility, viability, abnormality and acrosome integrity.L-arginine Supplementation at 0.5(G2) or 1.0%(G3) significantly (P<0.05) improved epididymal spermatozoa characteristics, as  % of motility, livability, acrosome integrity while, % of dead and abnormal spermatozoa decreased in supplemented groups as compared with G1. This improving was greatest in G2 than that happened in G3. Measurements of testes and epididymis increased in G2 and G3 compared with G1 . In addition, there was a significant increase of immunoexpression of testicular Nitric oxide synthase (NOS) in rams received L-arginine at 1% or 0.5% of body weight/day as compared to G1, and this expression was clearly found within the spermatid layer and few sertoli cells in both treated groups, while in G1, it was limited to spermatid layer only. . It could be concluded that dietary  L- arginine supplementation to Ossimi ram ration has positive effects on epididymal spermatozoa characteristics, Sexual organs anthropometries and immunohistochemical expression of testicular NOS.