Background Up to now there have been no satisfactory drugs to treat psychiatric disorders, and now bioactive compound from entomagenous fungi (BCEF0083) is a new type of bioactive compound from entomopathogenic fungi. Our previous investigations have shown that BCEF has an inhibition effect on monoamine oxidase. So, BCEF may be a latent antidepressant. This study aimed at observing the antidepressant effects and its mechanism of BCEF in the chronic unpredictable stress models in mice. Methods The antidepressant effects of BCEF were examined on the chronic unpredictable stress models in mice. Sixty mice were randomly divided to six groups. Animals were housed and isolated except saline group. Mice were exposed to different stressors per day randomly from day 1 to day 21. Body weight were weighed on day 1,day 10 and on day 21 during the 21-day stress procedure. Awarding response was detected by using method of calculating the 24-hour consumption of saccharum water. Step through test was used to evaluate the behavioral response. AVP contents in plasma were also detected by using radioimmunoassays. Results Chronic unpredictable stress resulted in a significant decrease of the body weight and could apparently cause escape behavior disturbance and gradual reduction of sensitivity to reward in animal models. Drug treatment (BCEF 25, 50, 100 mg/kg) could significantly ameliorate the decreased body weight and effectively reverse the escape behavior disturbance. The gradual reduction of sensitivity to reward, the anhedonic state, was also effectively reversed by BCEF. BCEF (50, 100 mg/kg) could also effectively restore the AVP content in the plasma.Conclusions This evidence suggests that BCEF can effectively inhibit the depression behavior and show strong antidepressant effect. BCEF can effectively restore the plasma AVP release and this may be an important mechanism of its antidepressant effect. Background Up to now there have been no satisfactory drugs to treat psychiatric disorders, and now bioactive compounds from entomagenous fungi (BCEF0083) is a new type of bioactive compound from entomopathogenic fungi. Our previous investigations have shown that BCEF has an inhibition effect on monoamine oxidase This study aimed at observing the antidepressant effects and its mechanism of BCEF in the chronic unpredictable stress models in mice. Methods The antidepressant effects of BCEF were examined on the chronic unpredictable stress models in mice. Sixty Mice were exposed to different stressors every day randomly from day 1 to day 21. Body weight were weighed on day 1, day 10 and on day 21 during the 21 -day stress procedure. Awarding response was detected by using method of calculating the 24-hour consumption of saccharum water. Step through test was used to evaluate the behavioral response. AVP contents in plasma were also detected by using radioimmunoassays. Results Chronic unpredictable stress resulted in a significant decrease of the body weight and could could apparently cause escape behavior disturbance and gradual reduction of sensitivity to reward to animal models. Drug The gradual reduction of sensitivity to reward, the anhedonic state, was also created by BCEF. (BCEF 25, 50, 100 mg / kg) could significantly ameliorate the decreased body weight and effectively reverse the escape behavior disturbance. BCEF can effectively restore the plasma AVP release and this may be an important mechanism of its antidepressant effect.