Objectives: This study aims to evaluate the effect of a mixture of fennel and valerian extracts on hot flashes and sleep disorders of postmenopausal women in Iran. A randomized trial was conducted. Methods: A total of 76 postmenopausal women were randomly assigned to either of the two groups: fennel-valerian extract or control.One 500 mg fennel-valerian extract capsule was given twice, daily for 8 weeks. The 500 mg oral placebo capsule (starch) was given the same way. Results: The mean duration of hot flashes increased in both the groups over time (P < 0.001). The mean frequency and severity of hot flashes in the intervention group were significantly lower than in the control group, in the first and second months after intervention (P < 0.050). Women in the fennel-valerian extract group had a significantly lower Pittsburgh Sleep Quality Index score than the control group 2 months after intervention (P = 0.030). Conclusions This study found that fennel-valerian extract was effective for relieving sleep disorders as well as the severity and frequency of hot flashes compared with a placebo.