Background: Long-term behaviour change in type 2 diabetic patients may provide effective glycemic control. Purpose: To investigate the key factors that promote behaviour change in diabetic subjects using the transtheoretical model. Methods: Subjects were selected by purposive sampling from type 2 diabetes outpatients. Self-administered questionnaires were used to collect the data related to the stages of behavioural change. HbA1C values were measured to evaluate glycemic control. Data were analyzed with analysis of variance (ANOVA), multiple regression and multinomial logistic regression. Results: Routine management of diabetes was a key factor in behaviour change, which correlated indirectly with HbA1C values through compliance and was positively affected by social support. Undermining from family or friends was directly associated with HbA1C. Conclusions: Based on factors influencing stages of behaviour change in diabetic subjects, tailoring a programme to help patients balancing life-style with diabetes, strengthening the patients' perceived confidence in routine management, and establishing a patient-friendly environment as well as support systems may show promise for changing the behaviours in all diabetic patients. (Contains 5 tables, 1 figure, and 1 note.)