Objectives: This study measures the association between hospital staff’s job strain (JS), mental quality of life (MQL) and how they are influenced by the organization models within emergency and critical care units. Material and Methods: This study describes workers employed in emergency departments and intensive care units of a French public hospital. A selfadministered questionnaire was used to survey the demographic and organizational characteristics of their work, as well as work-related mental stress, psychosocial and organizational constraints, and their MQL. Results: Among 145 workers participating in the study, 59.3% of them report job strain and 54.5% of them have low MQL scores. The majority of staff with job strain has reported working more than 2 weekends per month, were regularly on-call, worked in dysfunctional environments and did not participate in regular meetings. The staff with low MQL worked more frequently in dysfunctional environments, had significant complaints regarding employer’s efforts to promote communications or provide adequate staffing levels than the workers with a high MQL score. Conclusions: If stress reduction and improved MQL in emergency and intensive care units is to be achieved, hospital management needs to design work schedules that provide a better balance between working and non-working hours. Additionally, ergonomic design, functional environments and improved communications needs to be implemented.