This study examined determinants of the mean age at menarche (MAM) in 2 rural counties (Zongyang and Huaining) of Anhui province, China. Data were obtained from a 1993 household community survey among about 12,727 Han women. Years of age were adjusted to account for the Chinese lunar calendar. Analysis pertains to 5-year birth cohorts during 1949-78 compared to all cohorts born before 1949. MAM declined from 16.5 years to 13.7 years over a 40-year period. The trend was linear. Year of birth and level of education were strongly related to a decrease in MAM. MAM was also significantly associated with county, physical labor, general health status, exposure to pesticides before age at menarche, and water source. Year of birth explained most of the difference in MAM. There were no significant interactions between birth year and literacy, water source, or pesticide exposure, or between county and amount of physical labor. Women from Zongyang county had a later MAM than women from Huaining. Illiterate women had a higher MAM than literate women. The decline in MAM is attributed to improved nutritional status and living standards since World War II. 788 women reported a MAM that was older than 19 years. Subtracting these women only resulted in a decrease in MAM to 15.9 years for the pre-1949 cohort. Findings suggest a similar MAM for Anhui province as for China as a whole.