Desistance as a process to forgo delinquent habits is an important target for intervention into youth at risk of delinquency. The intervention through social work services, nevertheless, has not clearly demonstrated its effectiveness. For such a demonstration, the present study examines the contribution of social work services with reference to the voluntaristic theory of action. The theory suggests that promoting the youth’s voluntarism underlying desistance, encompassing appreciation, facilitation, observation, and identification concerning desistance is essential. The suggestion leads to the hypothesis that social work services promote the youth’s desistance through the promotion of voluntarism for desistance. This hypothesis gets support from this study of 586 at-risk youths in Hong Kong, with data collected from both the youths and their responsible social workers. The support implies the value of social work services for sustaining the youth’s desistance.