University students are particularly vulnerable to stress due to the demands of higher education and the developmental transition from adolescence to adulthood. The adverse effects of prolonged stress responses highlight the importance of the development of coping skills. Relaxation appears as a tool capable of restoring the resources depleted by stress and increasing positive emotions,cultivating also self-compassion. This study aimed (1) evaluate the effectiveness of a relaxation training program in university students, using a randomized controlled trial comparing an active control group (exposed to listening to relaxing music) and a passive control groups (without any intervention), considering the changes over time in depression, anxiety and stress; (2) to examine how selfcompassion and subjective happiness contributed to depression, anxiety and stress in the full sample; (3) and to examine the moderating role of self-compassion in the association between happiness and depression, anxiety and stress. Anxiety and stress increased for participants in the relaxation training program, alluding to the possible side effects of the initial practice. Higher levels of self-compassion and subjective happiness were both associated with lower levels of depression, anxiety and stress. Programs aimed at increasing self-compassion and subjective happiness seem to be relevant to promote students’ mental health.