With traditional in-person classes canceled due to the pandemic, teachers moved classes online, adapting new teaching methods. With this background, this study is aimed at exploring if flipped learning conducted through fully online systems improves students’ self-directed learning attitudes. Comparing a conventional flipped learning model with asynchronous online before-class sessions to offline during-class ones, this study replaced offline during-class sessions with synchronous online ones and tried to see if a variant form of flipped learning will be effective in promoting students’ self-directed learning attitudes over time. Twenty-two English major students participated in a variant of flipped learning for eight weeks. A pre- and a post-test were administered using a survey questionnaire adapted from Lee and Pyo (2018)’s four characteristics of self-directed learning attitudes: autonomy, responsibility, creativity, and self-concept. The research findings are as follows. First, there was a significant increase in all four characteristics of self-directed learning attitudes in the fully online flipped classroom. Second, two themes, ‘greater work efficiency online’ and ‘a unique group mechanism online’ were found from open-ended questions, and explain well why the online-only flipped learning model is conducive to developing students’ self-directed learning attitudes.