Abstract: Monthly distribution of menarche of 8 groups of schoolgirls in Inner Mongolia Autonomous Region was investigated. Results shown are that all of the 8 groups give characters of double peak in monthly distribution curve of menarche. One peak in winter (September-Feburary), another in summer (June-August). The appearance of the double peak character, concerned spirit factors, body lipoid and variation of the sunshine. Season distribution of menarche is affected by hereditary factor. Difference between the months of different groups in which the peaks located is affected by environmental factor.

Key words: Menarche; Monthly distribution; Group; Inner Mongolia