OBJECTIVE: To investigate the histomorphmetric alterations induced in the testicular tissues by variable sizes of SNPs. STUDY DESIGN: Male mice (BALB/C) were treated with SNPs (1mg/kg) using five different sizes (10, 20, 40, 60 and 100 nm) for 35 days. T esticular biopsies from all mice under study were subjected to histo morphological examinations. RESULTS: Silver NPs (10 and 20 nm) had provoked morphome tric changes in the testes of the subjected mice together with the following histo logical alterations: seminiferous tubules degeneration, spermatocytes cytoplasmic vacuolation, spermatocytes sloughing and spermatid giant cells formation. Larger SNPs (40, 60 and 100 nm) induced little or no testicular histomorphometric alterations. CONCLUSION: The findings of the present work may indicate that SNPs sub- chronic exposure could induce deleterious impacts on the testicular tissues and spermatogenic process that could affect fertility and reproduction, with smaller SNPs are more toxic than the larger ones.