text: INTRODUCTION: Garlic (Allium sativum), traditionally being used as a spice worldwide, has different applications and is claimed to possess beneficial effects in several health ailments such as tumor and atherosclerosis. Garlic is also an immunomodulator and its different components are responsible for different properties. The present work aimed to assess the effect of protein fractions of garlic on peritoneal macrophages. MATERIALS AND METHODS: 14-kDa and 47-kDa protein fractions of garlic were purified. Mice peritoneal macrophages were lavaged and cultured in a microtiter plate and exposed to different concentrations of garlic proteins. MTT assay was performed to evaluate the viability of macrophage. The amount of nitric oxide (NO) was detected in culture supernatants of macrophages by Griess reagent and furthermore, the cytotoxicity study of culture supernatants was carried out on WEHI-164 fibrosarcoma cell line as tumor necrosis factor-a bioassay. RESULTS: MTT assay results for both 14-kDa and 47-kDa protein fractions of stimulated macrophages were not significant (P   >   0.05). Both 14-kDa and 47-kDa fractions significantly suppressed production of NO from macrophages (P   =   0.007 and P   =   0.003, respectively). Cytotoxicity of macrophages' supernatant on WEHI-164 fibrosarcoma cells was not affected by garlic protein fractions (P   =   0.066 for 14-kDa and P   =   0.085 for 47-kDa fractions). CONCLUSION: according to our finding, 14-kDa and 47-kDa fractions of aged garlic extract are able to suppress NO production from macrophages, which can be used as a biological advantage. These molecules had no cytotoxic effect on macrophages and do not increase tumoricidal property of macrophages.