In the article, construction of incapacity of a human with mental disabilities is being analyzed on the basis of the experience of social workers. A critical viewpoint towards institutionalized social reality of incapacity construction based on the knowledge practices is being presented; reflexive nature of social work and dialogic relationship are being actualized. The research was conducted in 2013, by questioning six social workers from Klaipeda. For the research target, criterion-selection as well as social workers working with people with mental disability and involved in the incapacity recognition process were chosen. Qualitative research recognition object is based on the phenomenological strategy when other people’s experience is borrowed to reveal the phenomenon under investigation. For the data collection an interview method was chosen. The results of the research were presented by carrying out qualitative content analysis. The results show that the social workers are faced with professional dilemmas when confrontations between their thought, feelings and behavior appear. In the cognitive level, the social workers encounter with labeling and stigmatization of a human with mental disabilities in society, their devaluation in the near environment, mental disability identification with incapacity. In sensual level, social workers in relation to the client are confronted with professional role discrepancies, when on the one hand it is important to protect the client’s rights and interests, and on the other hand, there is the lack of institutionally regulated power to represent a human with mental disabilities. In collegial relationships with experts social workers feel themselves unequal, in a supernumerary role. In behavioral level, social workers confront with possible violations of human rights when a human with mental disabilities is not familiarized with their case, does not participate in the selection of a patron, involuntarily is placed in a foster home or the institution does not assume patronage. In the article the author presents recommendations in which perspectives of a social worker to reduce vulnerability of a human with mental disabilities are foreseen.