Melatonin has been implicated in skin functions such as hair growth cycling and skin pigmentation. Furthermore, melatonin receptors are expressed in several skin cells. To study the association between serum melatonin levels and skin aging grades among people aged 20-69years in Ulaanbaatar city. We performed an analytical cross-sectional study that used parametric testing through analyses to test the relationship between melatonin levels and skin aging grades. A total of 946 people were assessed for skin aging using a moisture checker, sebum tape, and a digital camera. Blood samples were collected between 8:00am and 10:00am, and melatonin was measured using an enzyme-linked immunosorbent assay analyzer. There was a statistically significant association between age and skin aging grade (P<.001). A multiple factor analysis revealed that lower levels of melatonin in the serum increased with skin aging grade 4 (odds ratio [OR], 1.9; 95% confidence interval [CI], 0.4-8.0), (OR, 2.4; 95% CI, 0.5-9.5), grade 5 (OR, 3.8; 95% CI, 0.8-15.7), and grade 6. There were weak associations between melatonin levels and potential covariates (skin pigmentation and skin hydration) taken from the correlation matrix. There was a weak positive correlation between skin pigmentation and age (r=.28), a weak negative correlation between skin pigmentation and sleep status (r=-.20), and a weak negative correlation between skin hydration and age (r=-.27). Serum melatonin decreases with age, indicating that its loss may stimulate the process of earlier skin aging.