This study aimed to investigate the effectiveness of health-promoting lifestyle (HPL) training on the mental well-being, vitality, and quality of life (QoL) of the elderly with diabetes. This was a quasi-experimental study based on a pre-test-post-test design with experimental and control groups. The statistical population consisted of all elderly with diabetes who were members of the Diabetes Association of Ahvaz in 2021, of whom 40 elderlies were selected as the sample through the convenience sampling method. The participants were randomly assigned to experimental and control groups. The participants in the experimental group attended eight 90-min sessions of HPL training. The data were statistically analyzed using the multivariate analysis of covariance in SPSS-17. The mean ± SD of the post-test scores of mental well-being, vitality, and QoL was 39.90 ± 4.80, 23.00 ± 3.31, and 35.00 ± 6.13 in the experimental group and 33.85 ± 4.81, 17.80 ± 3.15, and 29.15 ± 4.67 in the control group. The post-test results revealed a significant difference between the two groups in all of these three variables, as the HPL training significantly improved the mental well-being, vitality, and QoL of participants in the experimental group. Health professionals are recommended to apply HPL training, along with other training and therapeutic methods, to improve the health-related characteristics of such patients.