Positive effects of teacher-student relationships (TSR) have been widely documented. However, fewer studies have explored the determinants of TSR. The present study examined the effect of a possible determinant of TSR whose role has not yet been investigated -- teachers' compassionate love. It also examined the mediating role of teachers' compassionate love in the link between teachers' perceived social support and TSR. A sample of teachers (N = 142) answered an online questionnaire including the compassionate love scale. Teachers' compassionate love predicted the closeness dimension of TSR, even after controlling for attachment style, subjective well-being, and teachers' gender. Teachers' perceived social support from co-workers predicted teachers' compassionate love and the "closeness" dimension of TSR. The connection between teachers' perceived social support from co-workers and the closeness dimension of TSR appeared fully mediated by both dimensions of teachers' compassionate love. Hence, teachers' compassionate love is a crucial factor in the way students experience school.