Family involvement in mental healthcare is a key ingredient in the recovery of patients with mental illness. Research on the attitudes of mental health nurses regarding family involvement in mental healthcare remains limited. This study aimed to examine factors that affect the attitudes of mental health nurses towards the importance of family involvement in mental health nursing care. A descriptive, correlational study with a cross‐sectional design was conducted with 162 mental health nurses at two psychiatric hospitals in Taiwan. Descriptive statistics, independent t‐tests, one‐way analysis of variance, and stepwise multiple linear regression analyses were applied to analyse data. Mental health nurses generally demonstrated positive attitudes towards incorporating families into nursing care. Older age, more clinical experiences in mental healthcare, and workplace (such as working in chronic psychiatric inpatient wards) were found to be key factors for mental health nurses' attitudes. Particularly, greater competence in working with families and job satisfaction were the most significant factors associated with positive attitudes of mental health nurses towards involving families as important in nursing care. Insight into correlates of mental health nurses' attitudes towards the importance of focusing on families in care is pivotal for targeted interventions to improve nurses' attitudes towards families and, thus, implement family engagement in mental healthcare practices.