Objective To investigate serum IgG subclass concentrations in the adult population of Hunan region,and the effects of age,gender and lifestyle on them.Methods Serum IgG1,IgG2,IgG3,IgG4 and IgG concentrations from 170 adults making a health examination were detected by the immunonephelometric assay.Results The concentrations (mean or median [P25,P75]) of serum IgG1,IgG2,IgG3,IgG4 and IgG were (7.53 ± 0.14) g/L,3.99 (3.13,5.02) g/L,0.49 (0.30,0.70) g/L,0.53 (0.26,0.93) g/L and 12.2 (10.5,14.1) g/L,respectively.The serum IgG1/IgG,IgG2/IgG,IgG3/IgG and IgG4/IgG were (61.3 ±0.69)％,33.38％ (27.8％,38.8％),3.97％ (2.5％,5.3％) and 4.44％ (2.1％,7.3％),respectively.The serum IgG3 concentrations and IgG3/IgG ratios in female adults were significantly higher than that in male adults (P =0.005 and 0.014).However,there were no significant difference in serum IgG1,IgG2 and IgG4 concentrations and IgG1/IgG,IgG2/IgG and IgG4/IgG ratios between male and female adults.The serum IgG3 concentrations in the 31-40 years old adults were significantly higher than that in the 41-50 years old (P =0.03),while there were no significant difference in serum IgG1,IgG2 and IgG4 concentrations between different age groups.The serum IgG1 concentrations in the adults with heavy smoking were significantly lower than that without smoking (P =0.023),while the serum IgG4/IgG ratios were the opposite (P =0.018).The serum IgG1 and IgG3 concentrations and IgG3/IgG ratios in the adults with midrange or heavy drinking were significantly lower than that without ethanol consumption (P =0.05,0.004 and 0.015,respectively).The serum IgG3 concentrations and IgG3/IgG ratios in the adults with low-risk metabolism syndrome were significantly higher than that with the high-risk (P =0.034 and 0.038).Conclusion Gender and age have the significant effect on serum IgG3 concentration.Heavy smoking may reduce serum IgG1 concentration and increase IgG4/IgG ratio.The decrease of serum IgG1,IgG3 and IgG3/IgG may be related to ethanol consumption.