OBJECTIVE: To investigate the histomorphometric alterations induced in testicular tissues by variable sizes of silver nanoparticles (SNPs). STUDY DESIGN: Male mice (BALB/C) were treated with SNPs (1 mg/kg) using 5 different sizes (10， 20， 40， 60， and 100 nm) for 35 days. Testicular biopsies from all mice under study were examined histomorphologically. RESULTS: SNPs sized 10 and 20 nm had provoked morphometric changes in the testes of the subjected mice together with the following histological alterations: seminiferous tubules， degeneration， spermatocyte cytoplasmic vacuolation， spermatocyte sloughing， and spermatid giant cell 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 subchronic exposure to SNPs could have a deleterious impact on the testicular tissues and spermatogenic process that could affect fertility and reproduction， with smaller SNPs being more toxic than larger ones.