Teaching adult learners is not an easy mission for instructors. Among many factors affecting adult learners' learning, motivation seems to be the most significant. Studies on adult learners' motivation, especially on Vietnamese ones who pursue political science programs to become leaders in government offices and in the private sector, are still limited. Accordingly, this current study was conducted to investigate what motivates adult learners to be successful in their learning. Forty-six instructors who have worked with adult learners in political science programs for at least five years participated in this study to provide their perceptions of adult learners' reasons for taking an advanced political science course. A sixteen-item questionnaire was used to collect the quantitative data on teachers' perception of learners' motivators, and two focus group interviews were conducted to gain an in-depth understanding of the motivators stimulating learners to get involved and thrive in their study program. According to the survey results, the instructor participants perceived the desire to serve the community and the country and the trust of beloved people as the primary motivators for encouraging adult learners to continue their learning. Additionally, personal advancement and self-interest were also believed to have a remarkable impact on adult learners' learning motivation. The research context contributes to an explanation of why these motivators were highly perceived as adult learners' motivators. The results also stated the important role of institutional support for them to stay focused on their learning and foster the values of their school comeback.