Background: Considering social cognitive theory and current literature about successful advance care planning in nursing homes, sufficient knowledge and self-efficacy are important preconditions for staff to be able to carry out advance care planning in practice. Aim: Exploring to what extent nurses’ knowledge about and self-efficacy is associated with their engagement in advance care planning in nursing homes. Design: Survey study as part of a baseline measurement of a randomised controlled cluster trial (NCT03521206). Setting/participants: Nurses in a purposive sample of 14 nursing homes in Belgium. Methods: A survey was distributed among nurses, evaluating knowledge (11 true/false items), self-efficacy (12 roles and tasks on 10-point Likert-type scale) and six advance care planning practices (yes/no), ranging from performing advance care planning conversations to completing advance directives. Results: A total of 196 nurses participated (66% response rate). While knowledge was not significantly associated with advance care planning practices, self-efficacy was. One unit’s increase in self-efficacy was statistically associated with an estimated 32% increase in the number of practices having carried out. Conclusions: Nurses’ engagement in advance care planning practices is mainly associated with their self-efficacy rather than their knowledge. Further research is necessary to improve the evidence regarding the causal relationship between constructs. However, these results suggest that educational programmes that focus solely on knowledge might not lead to increasing uptake of advance care planning in nurses.