Abstract: Objective To explore the difference in antioxidant capacity of different kinds of drinking water and its possible mechanism in vitro and in vivo.Methods Concentrations of calcium,magnesium,chloride,sulfate,and nitrate in pure,tap,and mineral water samples were measured,respectively,and the antioxidant capabilities of the drinking water samples in vitro were evaluated with free radicals scavenging capability for hydroxyl,superoxide anion,and diphenylpicrylhydrazy (DPPH).Sixty ICR mice (half male and half female)were randomly divided into three groups and supplied with pure water (control group),tap water and mineral water as drinking water,respectively.After 90 days,total antioxidant capacity (T-AOC),hydroxyl radical inhibition capacity,content of malondialdehyde (MDA)and activity of catalase (CAT),glutathione peroxidase (GSH-Px),total superoxide dismutase (T-SOD) in brain,heart,livers and kidney of the mice were determined.Results For the three kinds of water samples,the mineral water had the highest contents of calcium and magnesium and the tap water had the highest contents of chloride,sulfate,and nitrate;while the pure water had the lowest contents of those inorganic substances.The scavenging rates of hydroxyl radicals (45.60±6.69 and 55.78±3.85%) and superoxide anion radicals (16.62±7.50 and 17.24±6.46%)of tap and mineral water were higher than those of the pure water (38.37±5.13 and 0.26±4.29%)(both P<0.05),and the scavenging rate of hydroxyl radicals of mineral water was higher than that of tap water group(P<0.05).Compared with those of the mice with pure water,significant decrease in MDA (1.75±0.26 and 1.63±0.20 vs.2.20±0.27 nmol/mg prot) and significant increases in T-AOC (4.33±1.28 and 4.43±0.74 vs.2.20±0.37U/mg prot),hydroxyl radical inhibition capacity(51.43±15.27 and 59.13±10.74 vs.29.22±5.72 U/mg prot),CAT (134.78±22.34 and 156.46±19.81 U/mg prot vs.75.59±6.84),and GSH-Px (92.53±14.88 and 97.16±19.86 vs.44.93±12.82 U/mg prot) were observed in the kidney tissues of the mice treated with tap and mineral water (all P<0.05).In addition,T-SOD (148.31±21.47 U/mg prot) in the kidneys from the mice with mineral water was higher than that of with pure water (113.99±15.25 U/mg prot) (P<0.05).Conclusion The antioxidant capability of tap water or mineral water in vitro and in vivo (mice kidney tissues) is superior to that of pure water,and the capability of mineral water may be higher than that of the tap water.