This present dissertation brings forward a reflection about the practice of Social Service and its connection with the mental health field, taking as a starting point the speech of social workers that are involved in mental health services in the city of Niterói. This study, of quantitative purpose, has sought to know how the practice of Social Service has developed in Mental Health, its specifications, challenges and contribution to a field that is known for its interdisciplinary quality. To accomplish it, we refer back to the history of the profession and its relation with this field, reflecting on the theoretical marks of the Brazil`s Movement for Psychiatric Reform and its implications in professional practice. We have sought to understand the process of the professionalization of Social Service, the challenges and hindrances faced by their professionals in the Mental Health field with the help of the Sociology of Professions. The analysis undertaken shows that interviewed professionals consider that the Mental Health field demands a more flexible attitude in their interventions, which indicates they have to pay a price, given that it means to not have the position they occupy defined in the referred field.