Adolescence is a transitional stage in human development that occurs at puberty into adulthood. Contemporarily, is marked with early social and sexual exposures that result to health, psycho-social, and economic problems. An alarming number of adolescents are actively involved in premarital sexual practices, which negatively results to reproductive health challenges. This study determined the forms and prevalence premarital sexual practices among secondary school students in Mayo-Belwa L.G.A, Adamawa State, Nigeria. Quantitative and qualitative method of data collection was adopted for the achievement of the study objectives. Quantitatively, through self-administration of 400 semi-structured and pre-tested questionnaires, a multi-stage sampling technique was used in selecting study participants, and data were analyzed descriptively. Qualitative data was generated through Focus Group Discussions (FGDs) and In-Depth Interviews (IDIs) among 106 purposively selected participants and analyzed thematically.  Among the 395 returned responses’ during questionnaire survey, more than a half 206 (52.2%) were females and 189 (47.8%) were males. The prevalence of premarital sexual intercourse had an alarming rate of 273 (69.1%), as 187 (47.3%) had been exposed for about 1–2 times, as 86 (21.8%) had three or more times. 41 (10.4%) had anal sex, 76 (19.2%) had had oral sex, and 305 (77.2%) had ever masturbated. Among the 206 female respondents, 18.0% had practiced genital rubbing. Conclusively, the prevalence of sexual intercourse and masturbation practices are high; couple with other forms of sexual practices. Therefore, the study recommends that there should be sensitization to inculcate abstinence and chastity, provide adolescents with the right decision making skills, and with reproductive health education.