BACKGROUND: We aimed to assess the in vitro effects of the green synthesized silver nanoparticles via thyme against infection. METHODS: We have prepared silver nanoparticles (TSNPs) by adding extract to the silver nitrate aqueous solution (0.2 mM), and evaluated their antileishmanial activity. The viability of promastigotes was assessed in the presence of various concentrations of TSNPs by direct counting after 24 h. The MTT assay was used to identify the viability of promastigotes. The same procedures were assessed in uninfected macrophage cells. The apoptotic effects of nanoparticles on promastigotes were determined by flow cytometry assay using annexin staining. To evaluate anti-amastigotes activity of TSNPs, light microscopic observation was used to determine the number of parasites within the macrophages in each well. RESULTS: The effect of TSNPs on promastigotes and amastigotes of . was effective and had a reverse relationship with its concentration. TSNPs, inhibited the growth rate of amastigotes and, the IC50 value of these nanoparticles was estimated 3.02 μg/mL (28 μM) after 72h. The results of flow cytometry showed that the toxic effects of TSNPs on promastigotes after 24 hours were statistically significant (<0.05) and showed 69.51% of apoptosis. CONCLUSION: TSNPs had an inhibitor effect on promastigote and amastigote forms of in vitro. It might be considered as a candidate for the treatment of this infection.