Background: Matricaria chamomilla (chamomile) is a herb used to treat various human illnesses. The present study was conducted to investigate the effects of chamomile extract on spermatozoon quality, serum levels of estradiol and testosterone, and sperm tail length in male adult rat. Methods: Male Sprague-Dawley rats received extract of chamomile (400 mg/kg once daily, orally) during an 8-week period, while the control animals received water. After this period, the animals were sacrificed and the blood samples were obtained. The serum levels of testosterone, estradiol, and the number, motility, and morphology of spermatozoon were assessed. The spermatozoon tail length was assessed by a rapid stereological method. Results: The body weight, and weight, and volume of the testis in the control and experimental rats did not change significantly. Serum testosterone level was decreased (~76%, P<0.005) and the serum estradiol level was increased (~16%, P<0.04) in the experimental animals. The spermatozoon count and motility were decreased in the experimental group but spermatozoon morphology did not show significant changes. The mid-piece and total tail length were reduced in the experimental group (~22%, P<0.001). Conclusion: Matricaria chamomilla extract can decrease spermatozoa count and motility, spermatozoon tail length, serum testosterone level and increase serum estradiol level in male adult rat.