Objective: Few studies have examined whether number of births is associated with women’s aging. This study aims to evaluate the association of number of births with women’s biological aging, premature mortality and life expectancy. Methods: A total of 272,494 participants from UK biobank who completed the questionnaire on number of live births were enrolled at baseline. The number of births was categorized into 6 groups, and participants with one live birth was the reference group. General linear regression model and cox proportional hazards model were performed to evaluate the association of number of births with women’s biological aging and premature mortality. Restricted cubic spline (RCS) was used to visualize dose-response relationship. Moreover, the latest Office for National Statistics life tables rom was used to calculate the life expectancy. Results: During a median follow-up of 11.9 years, a total of 10,992 cases of all-cause premature death were documented. After adjustment for potential confounders, compared to women had one birth, childless women had greater premature death (hazard ratio, HR=1.17, 95%CI: 1.09-1.25), whereas women with two or three children had lower risk of premature death (HR=0.87, 95%CI:0.82-0.93, HR=0.90, 95%CI: 0.82-0.99), which showed a U-shaped relationship visualized by RCS (P<0.05 for non-linearity). Further, at age 40, childless women had 1.41 years lower life expectancy, and women with two children was related to 1.10 years higher life expectancy. Moreover, compared to women had one birth, the women with two or three children had lower corrected estimated values of FI, ΔKDM-biological age and HD, and the women with five or more children had higher corrected estimated values of FI, ΔKDM-biological age, and HD (all the P<0.05). Conclusions: The association of number of live births with women’s biological aging, premature mortality and life expectancy had a U-shape relation. The childless or five more child women were more likely to be aging with increased risk of premature death and decreased life expectancy years. The double-child women decreased aging process with lower risk of premature death and high life expectancy.