To study adverse effects and underlying mechanisms of beta-cypermethrin (β-cyp) on male reproductive system, the 15-day intact male adult Sprague-Dawley (SD) rats assay was used as an in vivo test. Male adult SD rats were treated by oral gavage with 0, 15 and 30mgβ-cyp/kgBW for 15 days. After 15-day treatments, the testes, epididymis and seminal vesicles were excised and weighed, respectively. One testis was used for testicular sperm head counts, and the other was for immunohistochemistry test to characterize the expression of androgen receptors (ARs). There were substantial decreases of both sperm head counts and daily sperm production after β-cyp exposure. The expression of AR decreased significantly in rats treated with 15 and 30mgβ-cyp/kgBW, and the gray scale pixel values in the three groups (0, 15 and 30mgβ-cyp/kgBW) were 113.79±13.58, 96.09±5.95 and 77.27±5.44, respectively. These findings suggested β-cyp has significant adverse effects on the reproductive system. Reducing the expression of AR is a potential mechanism of decreased sperm production caused by β-cyp.