Objectives: Currently, the materials involving portions and exchanges in diabetes dietary education are abstract and difficult to comprehend. To improve the efficacy of dietary education, a fi gurative and easy-to-use dietary portion mapping was designed. Moreover, a patent was registered on the design, then the design was applied to type 2 diabetes mellitus. The purpose of this research is to explore the effi cacy of dietary portion mapping. Methods: Research design and methods were purposive sampling and quasi-experimental methods. Sixty volunteers were recruited to participate in this study from a clinic in Taichung City, and divided into experimental and control groups by random assignment. There were 30 patients in each group. The experimental group followed dietary portion mapping for 12 weeks. The control group had access to regular primary care. A diabetic dietary KAP questionnaire was the assessment tool used to evaluate the effi cacy of the intervention. Results: The knowledge score was 63.4 in the experimental group and 49.1 in the control group (P < .05). The attitude score was 85.9 in the experimental group and 80.8 in the control group (P < .05). The practice score was 81.1 in the experimental group and 67.5 in the control group (P < .05). The HbA1C was improved in the experimental group.The average HbA1c was reduced from 7.58 ± 1.40 to 7.14 ± 1.00 (P < .05) in the experimental group, but there was no signifi cant difference in the control group (P > .05). Conclusion: The intervention was effective with respect to knowledge, attitude, and practice of dietary control, and HbA1C control in the experimental group. The implication of this research can provide a reference for diabetes dietary education in the future.