Background: Nurses aim to improve QOL by supporting the proactive efforts of adults with diabetes. Although it is challenging to evaluate the influence of nursing, since it does not directly lead to improvement of symptoms and clinical indicators, we believe that it would be useful to examine the self-care ability inherent in patients. Instrument of Diabetes Self-Care Agency (IDSCA) aims to derive the direction of nursing based on the measurement results of the patient's self-care ability. This study examines the association between self-care ability and QOL as part of efforts to provide better nursing. Aim: To elucidate the factors of self-care ability in adults with diabetes related to QOL. Method: We conducted a questionnaire survey of adults with diabetes using IDSCA and SF-12 Health Survey. IDSCA contains eight factors, and the higher the score, the greater the self-care ability. For the analysis, descriptive statistics, simple regression analysis, and multiple regression analysis were performed. This study was approved by the Yukinoseibo-kai Social Medical Corporation Research Ethics Review Committee. Results: Overall, there were 139 respondents, 71 males (51.0%), 117 type 2 diabetes (84.1%), average age 62.8 ± 11.7, average duration of living with diabetes 16.1 ± 10.4 years, and average HbA1c value of 8.0 ± 1.1%. The average self-care ability was 153.6 ± 22.5 points. In simple regression analysis, four factors of self-care ability were influenced by age. In multiple regression analysis, the age × gender interaction term was examined, and a significant difference was found in the mental component summary (MCS) of QOL. Accordingly, we divided the subjects into four groups by age (under 65, 65 and over) and gender, and repeated the multiple regression analysis. Consequently, the self-care ability related to MCS was stress-coping ability (β = 0.36, p < 0.05) in the male group aged below 65; stress-coping ability (β = 0.34, p < 0.05), ability to make the most of the available support (β = 0.33, p < 0.05), and application or adjustment ability (β = 0.32, p < 0.05) in the female group aged below 65; stress-coping ability (β = 0.66, p < 0.01), ability to make the most of the available support (β = 0.40, p < 0.05), application or adjustment ability (β = 0.38, p < 0.05), ability of self-management (β = 0.52, p < 0.01), and body self-awareness (β = 0.40, p < 0.05) in male group aged 65 and over; and stress-coping ability (β = 0.66, p < 0.01), ability to make the most of the available support (β = 0.57, p < 0.01), application or adjustment ability (β = 0.41, p < 0.05), motivation to self-management (β = 0.42, p < 0.05), and ability of self-management (β = 0.59, p < 0.01) in the female group aged 65 and above. Discussion: It was revealed the self-care ability associated with MCS differs depending on the age and gender of the patient. With the maintenance and improvement of mental QOL, it was suggested which self-care ability would lead to better nursing. Acknowledgement: This work was supported by JSPS KAKENHI Grant Number JP16H05575.