OBJECTIVE Hot flashes are common experience for menopausal women, and for many, are severe enough to significantly compromise their overall sense of well being and quality of life. The aim of this study was to compare the efficacy of evening primrose with placebo in improvement of menopausal hot flashes. METHODS In a 6-week randomized clinical trial, a total of 56 menopausal women aged 45-59 years were participated in this study. The patients were asked for their hot flashes characteristics and responded to HFRDIS (hot flash related daily interference scale) questionnaire before and after the intervention. The participants were randomly assigned to take two capsules per day (totally 90 capsules for 6 weeks) of placebo or evening primrose (500 mg) for continuous 6 weeks. Then, the improvement in hot flashes was compared between two groups. RESULTS The percent of improvement in hot flash frequency, severity and duration were 39, 42 and 19 %, in evening primrose group compared with 32, 32 and 18 % in placebo group, respectively. Although all three characters of hot flash was ameliorated in evening primrose arm, only its severity was significantly better in this arm compared with placebo group (P < 0.05). All HFRDIS score were significantly improved in two groups, but the percentage of improvement in social activities, relations with others, and sexuality was significantly superior to placebo group (P < 0.05). CONCLUSIONS The application of oral evening primrose oil compared with placebo for controlling hot flashes may decrease more the intensity of attacks as well as ameliorating the HFRDIS score.