Aim: Patient education that enhances one's self-management ability is of utmost importance for improving patient outcomes in chronic diseases. We developed a 12 month self-management education program for type 2 diabetes, based on a previous 6 month program, and examined its efficacy. Methods: A randomized controlled trial was carried out on outpatients with type 2 diabetes from two hospitals who met the criteria and gave consent to participate. They were randomly divided into an intervention group that followed the program and a control group that followed usual clinical practise. The intervention group received <30 min of monthly interviews based on the program's textbook and biweekly telephone calls from a nurse educator throughout the 12 months. Results: Of the 50 participants in the intervention group and the 25 participants in the control group, 42 and 23, respectively, completed the program (a completion rate of 84.0%). The body weight, HbA1c, self-efficacy, dietary and exercise stages, quality of life, diastolic blood pressure, and total cholesterol level were significant by two-way repeated-measures anova. As for changes over time within the groups, only the intervention group showed significant differences by Friedman's test. The complication prevention behaviors showed a high implementation rate in the intervention group. The overall evaluation of this program by the participants was very high and, therefore, they highly recognized the need for this type of program. Conclusions: Self-management education works successfully in relation to patients' behavior modification skills, degree of goal attainment, and self-efficacy, consequently improving their health outcomes.