Abstract: Objective To explore the joint reproductivetoxi city and its mechanism of benzene and form a ldehyde in male mice.Methods To tally 108 Kunming male mice were randomly divided in to 9 groups according to 3×3 factorial design.Different dose of form a ldehyde(0,5,10 mg/kg),benzene(0,100,400 mg/kg),and both form a ldehyde and benzene were separately given to the mice by gastric gavage for 5 successive days.A fter 35 days,the mice were sacrificed and their testicular organ coefficient,spermmortality,malformation rate,testicular morphosis changes,testicular cell apoptosis were observed and the activity of Na⁺-ATP ase and Ca²⁺-Mg²⁺-ATP ase,the content of Ca²⁺ and total antio xidant capacity in testicle were detected.Results The sperm mortality and malformation rate and testicular apoptosis rate in the mice of the highest dose of formaldehy de and benzene combination group were 18.56±2.83,22.03±1.35,9.76±0.76%,respectively,with signifiant increase compared to that of the control(P<0.01).The testicular morphosis was damaged,the activity of Ca²⁺-Mg²⁺-ATPase,Na⁺-K⁺-ATPase and the content of total antioxidant capacity were decreased;the content of Ca²⁺ was increased in testicles of the mice of treated groups.There was a significant dose effect relationship(P<0.01)compared with that of the control group.The joint toxic effect of benzene and form a ldehyde exhibited synergistic or additive effect.Conclusion Form a ldehyde and benzene have synergistic or additive toxic effect on reproductive system of male mouse.The mechanism may be related to the inhibition of the A T Pase activity,the impact of total antio xidant capacity,and the disbalance of Ca²⁺ in mouse testicle.