Abstract: Objective To observe the levels of serum oxidative products (MDA) and changes in the activities of antioxidases in the simulated high altitude dive,and also to study the effects of the high altitude dive on oxidative damage to the body.Methods Blood samples were collected from the simulated high altitude divers,before entrance into the chamber,during stay at high altitudes,upon completion of the dive and after surfacing from the chamber,for the detection of MDA,SOD,GSH-Px levels,the activities of antioxidases and catalase (CAT),and total anti-oxidative capacity (TAOC).Results The levels of MDA fluctuated within the range of ( 3.31 ± 1.35 ) ~ (6.98 ± 3.52 ) μmol/L.The activities of antioxidases were within the normal range.MDA levels and GSH-Px activities were directly correlated with the oxygen partial pressure and exposure duration.In the hyperoxic and hypoxic alternating environments,EPO levels were negatively correlated with the activities of SOD and CAT.Conclusions No oxidative damage induced by hyperoxic and hypoxic alternating environments could be detected in the 4 divers in the simulated heliox dive.