Background: Age at menarche is an important factor in health planning and reproductive health of females. Studies have indicated that girls are attaining puberty earlier than in the past. Objectives: To explore age at menarche and factors determining it among unmarried girls. Methods: This community based cross-sectional study was conducted in Rural, Urban and Slum strata of UT Chandigarh ,during April 08 to March 09 in total duration of 12 months .Stratified Multistage Random Sampling Design with probability proportional to size (PPS) was utilized. 744 respondents were selected and interviewed by personal interview method to collect desired information. Results and Discussion: The study showed, Maximum respondents 282 (37.9%) were found in the age group 13-15 years followed by 240 (32.3%) in the age group 16-18 years. Maximum number of respondents attained menarche between 13-14 years of age. Mean age at menarche was found to be varying significantly according to type of family (P__ampersandsignlt; 0.001), home environment (P __ampersandsignlt; 0.001), menstrual problems (P=0.03) and menstrual cycle (P=0.001). Respondents whose home environment was not religious, attained menarche significantly earlier (P__ampersandsignlt;0.001).This study reported several correlates of age at menarche but their casual relationship could not be established being a cross-sectional study. Menarche an event of the past, was investigated in this study and possibility of recall-bias cannot be ruled out.