Teacher turnover has been increasing nowadays and novice teachers often complain from the teaching load and confront burnout. Mentors, as well, lack sufficient mentoring skills and have negative perceptions toward mentoring; which affect their self-efficacy. Research on mentor perception and self-efficacy is also sparse. Therefore, this study aimed at exploring the effects of a mentoring preparation program on 15 Egyptian EFL in-service teachers' efficacy and perceptions of mentorship. The study sought to identify the benefits, barriers, and mentoring strategies during this six-week program. In this mixed-methods study, participants completed a Mentor Efficacy Scale (MES) and a perception questionnaire before the program. Participants filled out mentor logs reflecting on and reporting their activities with mentees. After the program, the MES scale, perception questionnaire, and semi-structured interviews were administered. Results showed that the greatest strengths of the mentoring program were empowering teachers professionally, improving communication and problem-solving skills, and using sustainable mentoring strategies. Participants used some mentoring strategies: setting goals, building effective relationships, observation and conferencing, peer-mentoring, and co-teaching. The study recommends building sustainability in professional development by designing contextual mentoring programs and cultivating mentoring culture in schools.