Aim: To investigate how nurses perceive tasks and responsibilities in physical activity promotion of hospitalized older patients and which factors are of influence. Design: Mixed methods sequential explanatory design. Methods: One hundred and eight nurses participated in a questionnaire survey and 51 nurses in a subsequent in-depth interview. Data were collected on tasks and responsibilities in physical activity promotion and their influencing factors as perceived by nurses. Quantitative data were analysed using descriptive statistics and a deductive approach with directed content analysis was used for the data from the interviews. Results: Nurses perceived to have a dominant role in physical activity promotion of older patients during hospitalization. Ninety per cent of the nurses stated to be responsible for physical activity promotion and 32% stated to be satisfied with the actual level of physical activity of their patients. Nurses have specified to be responsible for signalling and performing physical activity promotion tasks and had final responsibility for transfers from bed to chair and promotion of daily activities. Influencing factors were low patient motivation, high workload causing priority shifts of tasks and the role of physicians.