Mailing programs involve indirect supervision and are designed to enhance adherence to longterm exercise in older adults. However, it is unclear how such mailing programs help older adults to overcome barriers and adhere to an exercise program. The purpose of this study was to extract the effective factors of a mailing program based on mixed-method research. Community-dwelling adults aged 65 years or older (n = 78) participated in a 3-month exercise class that aimed to develop skills for behavior change, followed by a 12-month mailing program. During the 15-month study period, the participants were consistently advised to practice brisk walking, muscle strengthening, and stretching according to a self-determined schedule. They were also advised to set a monthly exercise goal, exercise daily, and record it in an exercise diary. At the end of each month, the participants mailed the exercise diary to instructors who provided feedback that included praise, suggestions, answers, recognition, sympathy, and encouragement. The instructors would return the diary to the participants along with an exercise newsletter consisting of scientific information on exercises, names of participants who had achieved their exercise goals, and comments from the participants themselves. The newsletter was designed to expand the participants’ knowledge about exercise, to provide social support, and to strengthen self-efficacy. For qualitative evaluation, 18 participants with various exercise adherence levels were invited for focus-group interviews and their comments were recorded and analyzed. Fifteen factors related to the mailing program (e.g., satisfaction about record-keeping, self-reflection, information obtained, praise, and advice) were extracted. The participants’ comments well reflected the goals needed for developing behavior change skills that were emphasized during the exercise class and the mailing program. For quantitative evaluation, a questionnaire was administered to understand the participants’ perception of the mailing program, and 60 of them responded. The results indicated that daily recording in the exercise diary (95%) and gaining knowledge through the scientific information provided in the newsletter (93%) were perceived as effective factors of the mailing program. In conclusion, our qualitative evaluation of the effectiveness of the mailing program revealed 15 factors that were congruent with behavior change skills. Quantitative evaluation revealed that the majority of older adults considered the mailing program to be effective for enhancing their long-term adherence to exercise. Therefore, the mixed-method approach used in this study contributed to knowledge on factors that support exercise adherence among older adults.