Major changes have taken place in psychiatric care in Sweden as well as in other countries. These changes, and the current climate of pressure and demands on the nursing staff in psychiatric in-patient care, make it important to be able to understand the relationship between environmental aspects and the nursing staff’s working conditions. The overall aim of the present thesis was to investigate perceptions of the ward atmosphere, the psychosocial work environment and stress among nursing staff working in psychiatric in-patient care. The findings were based on two questionnaire surveys (65 + 93 participants) and were analyzed using non-parametric statistics. The findings showed that a revised Swedish version of the Ward Atmosphere Scale involved some reliability problems that need to be addressed in future studies. Several aspects of the ward atmosphere were found to be related to the psychosocial work environment, and aspects of the ward atmosphere and the psychosocial work environment were related to the nursing staff’s Perceived Stress and Stress of Conscience. The nursing staff’s sense of Mastery was found to be a protective factor against Stress of Conscience, while a Sense of Moral Burden increased the vulnerability. Taking these aspects into consideration when making improvements in the workplace could help to prevent stress.