Online courses are popular around the world these days as people can access learning being in different times and spaces. At the same time, the retention of participants in any online course is always challenging. This qualitative case study investigated the issues related to participant retention in an online course and explored the effective ways to retain the participants in such courses. The data were collected through the interviews conducted with 12 teachers who partly or wholly participated in a year-long online course. Teacher participants’ online communication exchanges on Edmodo and Viber platforms during the course period also served as data for this study. The Edmodo and Viber extracts were originally in English while the interviews were conducted in Nepali; therefore, in the process of analysis, some key extracts were translated, especially focusing on the message they communicated. The findings based on thematic analysis reveal that the issues related to retention include facilitators’ delayed response, poor activity design and inappropriate selection of web tools, and need for additional time among others. This study is expected to assist course designers, institutions, and organizations that run online courses as well as teachers who plan to run and join online courses as they can be informed of the issues that play a role in the retention of participants in online courses.