During the COVID-19 pandemic, using online and flipped instruction is the best alternative for traditional instruction. Therefore, this study compared the effects of three instructions, including online, flipped, and traditional, on improving Iranian EFL learners’ vocabulary knowledge. To do so, 90 Iranian intermediate EFL learners were selected among 119 students as the participants of this study. The target participants were randomly divided into three equal groups (online, flipped, and traditional). After that, all groups were pretested by a vocabulary test. Then, the participants of one group received the treatment by using fully online instruction, and the other group participants received a flipped instruction. On the other hand, the participants of the third group received conventional vocabulary instruction. After teaching 100 new English words to all groups with three different instructions, a vocabulary posttest was administered to all participants. The paired samples t-test and one-way ANOVA results indicated that both online and flipped groups outperformed the control group in the vocabulary posttest. In addition, the findings revealed the flipped group outflanked the online group in the posttest of vocabulary. The implications of this study can encourage both EFL teachers and learners to integrate the flipped and online instructions into their teaching and learning processes.

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