This study was conducted to investigate the effect of two concentrations (0.5 and 1ppm) of silver nanoparticles on levels of serum FSH, LH and E 2 in PCO-induced female mice. A number(n=80) of mature female mice were intraperitoneally injected with human Chorionic Gonadotropin (hCG) at a dose of (10 IU/ mL) three days a week for two weeks in order to induce PCO. Then, these mice were divided into two groups, according to the duration of treatment (30, 45 days). Each group was subdivided to subgroups according to the substance administrated. Two subgroups were treated with (0.5 and 1ppm) of silver NPs solution by (i.p) injection twice a week and the third subgroup was treated with metformin at a dose of (1mg/day) orally three days a week. Results: there was a significant reduction (P<0.05) in serum levels of FSH in the PCO group treated with (1ppm) of silver NPs for 30 days as compared to the control. While, a significant elevation (P< 0.05) was observed in levels of E 2 , for the same group as compared to the control. The PCO group treated with (0.5ppm) recorded a significant reduction (P <0.05) in serum levels of E 2 for the same duration. But longer duration (45 days) exhibited a significant elevation (P< 0.05) in levels serum of FSH in the PCO-induced mice treated with (0.5ppm) of silver NPs which, was similar to the effect of metformin. A significant elevation (P> 0.05) in serum levels of FSH was observed in the PCO group treated with (0.5ppm) of silver NPs along 30 days as compared to their similar group that was treated along 45 days but, non significant alteration (P> 0.05) were observed in serum levels of LH or E 2 between groups of the (30 days) duration as compared to their similar groups of the second duration (45 days). Conclusion: World Journal of Pharmaceutical ResearchThere were significant alterations in levels of serum FSH, LH and E 2 in the PCO-induced mice treated with both concentrations of silver NPs as compared to the control.