Abstract Background/Introduction Heart failure (HF) self-care is important for the effective management of HF, reducing clinical events such as all-cause mortality and hospitalizations. HF self-care behaviours encompass comply with a regimen involving medication, diet, and exercise, symptom monitoring, and seeking assistance when symptoms occur. Frailty, prevalent among older patients with HF, involves physical, social, and cognitive domains. Identified factors influencing self-care behaviours in patients with HF include age, social support, and knowledge of the condition. Despite research on the association between self-care behaviours and frailty, there is a notable gap in studies that explore the relationship between self-care behaviour and multiple domains of frailty, particularly with adjustments for clinical characteristics. Purpose The aim of this study was to assess the association between self-care behaviour and multiple domains of frailty in older patients with HF. Methods The study included 182 patients with HF who were aged 65 years or older. Self-care behaviour was assessed 5 months after their discharge using the European Heart Failure Self-Care Behaviour Scale (EHFScBS), a self-report questionnaire. Frailty was assessed using the revised Japanese version of the Cardiovascular Health Study criteria (J-CHS) for physical frailty, and using Makizako’s five items for social frailty, and using Mini-Cog for cognitive decline. We used multiple regression analysis to assess the association between self-care score and multiple frailty domains and the number of frailty domains. The adjusted model was constructed based on age, gender, body mass index, New York Heart Association Classification, left ventricular ejection fraction, log-transformed B-type natriuretic peptide, estimated glomerular filtration rate and history of HF. In addition, we used multiple regression analysis to assess the association between the EHFScBS subitems score complying with regimen, asking for help, and adapting activities and multiple frailty domains and the number of frailty domains. Results According to the results of a multiple regression analysis, poor self-care behaviour was significantly associated with physical and social frailty and the number of frailty domains (all p < 0.05), even after adjusting for clinical characteristics. Poor complying with regimen was also significantly associated with physical and social frailty and the number of frailty domains (all p < 0.05). Poor asking for help was significantly associated with social frailty and the number of frailty domains (all p < 0.05). Conclusion The study indicates that poor self-care behaviour is linked to physical and social frailty, in addition to the cumulative number of frailty domains in older patients with HF, even when clinical characteristics are taken into consideration. This underscores the importance of factoring in the frailty status when guiding patients with HF in disease management.