School-based mentoring programmes in which teachers act as mentors have the potential to offer a non-stigmatizing and developmentally appropriate source of support for secondary school students. However, the experience of teacher-mentors is under-researched, particularly in Hong Kong. Fifteen mentors participating in a school-based mentoring programme in one Hong Kong secondary school serving a Chinese population were interviewed and the data were analysed thematically. Findings indicated that teacher-mentors provided social and emotional support to their mentees, and that they were motivated to do so by a desire for greater relatedness to the students with whom they worked. The relationship formed between mentors and mentees was more spontaneous, less hierarchical, more wide-ranging, and more personal in nature than that between teachers and students, and constituted a source of satisfaction for mentors. The study has several implications for schools which may be considering implementing a mentoring programme.