To investigate the toxic effects of inhaling cooking oil fumes (COF), 30 male SD rats were submitted to inhaling COF at a constant concentration and duration (35-53 mg/m3, 30 min/d) for different length of time (20, 40 and 60 days), and examined for change in body weight, spermtogenesis and content of trace elements in their testes. The results indicated that the body weight and the ratio of gonad to body weight in rats inhaling COF for 40 and 60 days were lower than those in the controls (P < 0.05). Fewer alive sperms and more malformed or dead sperms were fond in the epididymis of rats exposed to COF for 40 and 60 days. Among the four trace elements(Zn, Mn, Cu, Fe) studied, the content of Zn in the testis was found to be significantly decreased and that of Mn significantly increased in the rats exposed to COF for longer periods. There existed a time-effect relationship in all of the above findings. The results suggested that inhaling COF was significantly toxic to male gonads, and the imbalance of Zn, Mn might be contributive to the damage of testis.