The difference in bird's body condition may lead to the variation of reproductive success. Recent works have suggested that biomarkers of oxidative stress might provide an additional tool to assess the health state of individuals. Oxidative stress is usually defined as the imbalance between pro-and anti-oxidative processes. Oxidative stress is the physiological adaptation mechanism of individuals to cope with stress, that reflects the environmental conditions that birds experience. The oxidative status also a priori informative tool to evaluate the reproduction and survival of individuals. However, the conclusion about the role of oxidative stress on the reproductive of wild organisms is not consistent. In this study, to explore whether the plasma biomarkers of oxidative stress can predict the reproductive success of Varied Tit (Sittiparus varius), we took blood samples from the pairs of Varied Tit bred in the artificial nest boxes during their early brooding period (6﹣8 days post-hatching). Then we used the ELISA kit to measure the levels of plasma oxidative stress (reactive oxygen species, ROS and superoxide dismutase, SOD concentration). We also got the reproductive parameters of Varied Tit by nest monitoring. Partial least squares regression (PLS) analysis was used to analyze the relationship between oxidative stress and reproductive success (fledging rate and breeding success). We found that there are no significant differences between males and females in plasma reactive oxygen species and plasma superoxide dismutase concentration during chick-rearing period (independent- samples t-test: reactive oxygen species, t (20, 25) =﹣0.887, P = 0.380; superoxide dismutase, t(20, 25) =﹣1.325, P = 0.192). We also found that the plasma reactive oxygen species concentration was significantly negatively correlated with the fledging rate (partial least squares regression: B =﹣0.966, P = 0.013, Fig. 1 a) and breeding success (partial least squares regression: B =﹣0.976, P = 0.002, Fig. 2 a) of female Varied Tits, and females with a lower reactive oxygen species concentration tended to have a higher fledgling rate and breeding success. The reproductive success of female Varied Tit was not related to the plasma superoxide dismutase concentration, and there was no statistical significance in any analysis of males. Our findings suggest that reactive oxygen species, as a biomarker of oxidative stress in plasma, could be a tool to assess the fitness components and predict the reproductive success of female Varied Tits.