BACKGROUND There is growing concern that occupational, environmental and lifestyle factors adversely affect male reproductive health. Fumaria parviflora Lam. is being used traditionally in Persian folk medicine to cure various ailments and has been supposed to have fertility-enhancing properties. OBJECTIVE A dose-response study was designed to assess effects of F. parviflora ethanolic leaves extract on reproductive parameters in adult male Wistar rats. METHODS In this experimental study, healthy adult male rats were treated with 100, 200 and 400 mg/kg/day of F. parviflora leaves extract via gavage for 70 days. Blood samples were collected for determination of testosterone, LH and FSH serum levels. Reproductive organs weight, motility, morphology and density of epididymal sperm, seminiferous tubules diameter and germinal epithelium height were evaluated in each experimental group. RESULTS The body weight was not affected, while the weights of testis and epididymis were significantly enhanced in rats treated with 200 and 400 mg/kg/day F. parviflora extract. No significant changes were observed in seminal vesicle and ventral prostate weight between experiment groups. Significant increase was found in epididymal sperm density and percent of morphologically normal sperm in extract-treated rats. Serum testosterone levels were significantly higher in rats received 200 and 400 mg/kg/day. CONCLUSIONS The results indicated that ethanolic extract of F. parviflora leaves have a potential to improve reproductive parameters and enhance male fertility.