Early child bearing is a widely observed phenomenon in Nepal. However, little information is available in regard to its contributing factors. This retrospective exploratory study was carried out to determine factors contributing to adolescent pregnancy in rural Nepal. Cluster sampling technique was used to select the study settings. The findings on variable contributing to pregnancy from the sample of 575 mothers, who had their first pregnancy at an age below 19 years, were compared with the findings from an equal number of mothers who had their first pregnancy at the age of 20 years or above. The adolescent mothers were married at a comparatively younger age with a mean age of 15.9 years. Parents or elders, with/without the girl's consent, decided the majority of adolescent marriages. The age at marriage exposed women to early pregnancy regardless of who decided the marriage. Comparatively, most adolescent mothers were from a low social class, engaged in agricultural work, and they had low literacy rate. Majorities of the mothers from both groups had no prior knowledge about conception until they conceived. Peers were the main source of information regarding conception. Although the majority of the respondents knew at least one method of contraception, less than 1% had used it before their first pregnancy. To conclude, early pregnancy had put the adolescent mothers at the risk of unwanted pregnancy and obstetric complications. Women empowerment through compulsory girls' education would be the most effective strategy to prepare them for late marriage, planned and delayed pregnancy, and better motherhood.