Aims: This study aimed to assess the effectiveness of a health education program in increasing knowledge, promoting healthy behavior, glycemic control, and improving the quality of life of patients with diabetes mellitus.

Materials & Methods: This study used quantitative methods, a survey design, and data analysis using Structural Equation Modeling - Partial Least Squares in Surabaya from September to November 2024. Data were collected through questionnaires distributed to diabetes mellitus patients in the Gresik Regency. The sampling technique used cluster sampling, considering age, gender, and education level.

Findings: The health education program significantly improved patients' understanding of diabetes management. Knowledge scores increased significantly (p=0.038) after the intervention (4.2±0.8) compared to before (3.1±1.0). The adoption of healthy behaviors also increased (4.0±0.9; p=0.042). In addition, the program positively impacted glycemic control, with a decrease in mean HbA1c from 8.5% to 7.2% (p=0.044). Patients' quality of life improved significantly, both in physical and psychosocial aspects, with a difference in scores before (3.8±1.1) and after (4.5±0.7) the intervention (p=0.005).

Conclusion: Increased knowledge, adoption of healthy behaviors, glycemic control, and quality of life positively influence the effectiveness of the transtheoretical model health education program.