Background: Age at menarche and menopause is affected by various factors. A reduction has been observed in these ages over time. The present study aimed to determine the trend of changes in age at menarche and age at menopause among the women participating in Fasa Cohort Study over a 40-year period. Methods: This cross-sectional, descriptive-analytical study was conducted on 5545 women aged over 35 years in Fasa cohort population as a branch of the Persian cohort study. The participants were selected via census. The study data were obtained from the information registered in Fasa Cohort Center. Then, they were entered into the SPSS 22 software and were analyzed using descriptive statistics, chi-square test, correlation coefficient, and linear regression analysis. Results: The results showed that the mean age at menarche reduced from 14.66 to 13.40 years and the mean age at menopause decreased from 56.88 to 40.16 years over the 40-year period, and the reductions were statistically significant (p<0.001). Age at menarche was affected by body mass index and physical activity. Besides, age at menopause was affected by education level, marital status, diabetes, hypertension, cardiovascular diseases, cervical cancer, hysterectomy, and stillbirth (p<0.001). Conclusion: The results showed a decrease in age at menarche and age at menopause over the 40-year period.