Objective: Several factors appeared to influence the onset of menarche. The current study was aimed to determine the mean age of menarche and the factors influencing its onset among female high school students in Asmara. Methods: A cross-sectional study was conducted from January to February 2017 among secondary school female students of Asmara city. A 2 stage stratified sampling design was adopted to select the number of schools and students for the study. A structured and pretested questionnaire was used to collect the data through interview. Data analysis was done using SPSS version 22. Descriptive results were summarized using frequencies and percentages in tables and graphs. Moreover, bivariate and multivariate logistic regression analysis was done to find out the association of earlier onset of menarche and the predictor variables. Results: A total of 300 female students participated in the study. The mean age of the participants was 16.1 years (SD=1.3) with majority of them (57.3%) between the ages of 16 and 18 years. The mean age at menarche was 13.8 years (SD=1.2). About 39% of the participants have the onset of their menarche earlier (before 14 y). An earlier onset of menarche was observed among younger age (above 16) respondents {adjusted odds ratio [AOR] [95% confidence interval (CI)]: 1.8 (0.96, 4.88), P-value: 0.02}, having higher body mass index [AOR (95% CI): 3.8 (1.92, 7.85), P-value: 0.001] and from richer family. Lack of engaging in any kind of physical activity [AOR (95% CI): 2.56 (1.13, 5.27), P-value: 0.012] and more sleeping hours [AOR (95% CI): 2.2 (0.36, 4.18), P-value: 0.04] were also factors influencing earlier onset of menarche. Conclusion: The mean age at menarche was relatively low. Factors related to higher body mass index, physical inactivity, more sleeping hours, good socioeconomic status, and younger age were associated with earlier onset of menarche. Initiatives on awareness creation are required to increase lifestyle modifications at individual level.