This phenomenological study analyzed the advantages and disadvantages of online-activity-based instruction experienced by Korean language teachers during the COVID-19 pandemic. For this purpose, Colaizzi’s method was used in analyzing a video clip of a YouTube lecture(Mulkko TV). The advantages of online-activity-based instruction in the Korean language class were identified as automatic archiving of activity data, increased access to activity data, decreased presentation time, focused and intensified thinking, and reduced burdens of writing and presentation. The disadvantages include an unlively mood, lack of teachers’ involvement, lack of connection with other classmates, and restricted access to learning materials. While the disadvantages of online-activity-based instruction in Korean language classes are also commonly observed in other online classes, it offers greater advantages than in other subjects owing to the nature of the subject of Korean language. This study provides substantial examples of online-activity-based instruction in Korean language classes and provides specific information on their applicability.