Introduction In order to be effective in discussing high-risk sexual behaviors with adolescents, mothers need to be educated about their adolescent daughters’ sexual issues. As no detailed and exact knowledge on mothers’ educational needs concerning adolescent girls’ reproductive health is available, the current study was intended to investigate mothers’ educational needs concerning their adolescent daughters’ reproductive health. Materials and methods This research was a qualitative content analysis. Purposive sampling was performed to the saturation point. The samples included 26 mothers and 14 key informants. Semi-structured interviews were used for data collection. Data authenticity was verified based on Lincoln and Guba’s criteria and data analysis was conducted using conventional content analysis with MAXQDA10 software. Findings In this study, three themes and 13 main categories, each with a number of subcategories were extracted. The themes and main categories included: “appropriate educational content (reproductive health, sexual health, general health, psychological health, family health, social health and spiritual health)”, “characteristics of the educator (communicative skill, cognitive skill and moral competence)”, and “effective factors in learning (teaching method, learning conditions and environment, and the learner’s readiness)”. Conclusions The results demonstrated that mothers need to be informed about sexual, reproductive, general, psychological, family, social and spiritual health in adolescent girls. Consequently, the results can help the healthcare authorities to implement need-based programs and boost the effectiveness of education about adolescent girls’ reproductive health for mothers.