Background <p>Menarche, marking the onset of female reproductive potential. Understanding the secular trends in age at menarche (AAM) is crucial for public health, as earlier menarche is associated with adverse health outcomes in adulthood. This study sought to explore the long-term trends of AAM among Han Chinese females in Shanghai, China, and to explore its correlation with overweight/obesity in adulthood.</p> Methods <p>We utilized baseline data from the Shanghai Suburban Adult Cohort and Biobank (SSACB), a large-scale community-based study. A total of 38,396 Han females born between 1942 and 1995 were included. Participants were divided into 11 birth-year cohorts and five percentile groups (10th, 25th, 50th, 75th, and 90th) based on AAM. The overweight/obesity status was defined using BMI criteria. Quadratic and quantile regression analyses were conducted to evaluate the time trends of AAM.</p> Results <p>The mean AAM decreased from 17.45 ± 2.50 years in females born in 1942 to 14.20 ± 1.33 years in those born in 1995, with an average decline of 0.68 years per decade (<i>p</i> &lt; 0.001). This trend was consistent across all percentile groups, with the most significant decline observed in the 90th percentile group. Females who experienced a greater decline in AAM (a decrease of 0.076 years per year) had a higher prevalence of overweight/obesity (OO) — compared to females with a smaller decline in AAM (a decrease of 0.064 years per year), who were currently non-overweight/obese (NOO).</p> Conclusions <p>This study highlights a secular trend towards earlier menarche among Han Chinese females in Shanghai over the past half-century. Women with earlier menarche are more likely to be overweight or obese in adulthood, suggesting that earlier menarche may increase the risk of obesity in adulthood, and attention should be paid to early weight control intervention. Our findings provide valuable insights for public health policies aimed at improving Han women’s health in highly urbanized regions.</p>