question: Feedback is one of the key elements for students' online learning for it can be used to foster their knowledge and attainment. Nevertheless, the scrutiny of feedback with respect to WhatsApp amid the COVID-19 pandemic, to the best of the writers' knowledge, was still under-researched. Thereby, this study aimed to uncover the instructor feedback in a WhatsApp group. The embedded design of mixed-method was employed. Twenty-three EFL postgraduate students, taking an online course using a WhatsApp group in one university in Bandung city, were involved. Moreover, the data were garnered using a questionnaire and semi-structured interview corroborated by online chat archives in the WhatsApp group. Findings revealed that the use of WhatsApp resulted in some challenges and opportunities. Moreover, based on the content analysis, the most frequent level of instructor feedback encountered was self-level (64%) consecutively followed with process level (20%), task level (15%), and self-regulation level (1%). Additionally, descriptive statistics revealed that with a mean of 82.5 and a standard deviation of 6.5, the instructor feedback quality was categorized as a good one. Meanwhile, some themes concerning the instructor feedback characteristics found encompassed immediacy, relevancy, constructiveness, and objectivity. Some pedagogical implications and suggestions to optimize the use of WhatsApp as a learning tool were also discussed. © 2021 IEEE.