This study set out to compare the efficacy of first language (L1) equivalent versus contextualized vocabulary instruction on the vocabulary retention of EFL learners. In this study, forty-five English as foreign language (EFL) learners were divided into three groups, i.e., two experimental and one control group. The experimental groups used first language (L1) equivalent and contextualized vocabulary instruction. The first experimental group received Persian translation of the predetermine word, and the second experimental group received 60 sentences in which they were asked to fill the gap using target words. The words are considered to be the most frequent vocabularies extracted from reading passages of the students' textbooks. Before the intervention, a pre-test of vocabulary was conducted to check the students’ knowledge of vocabulary. The data were collected during a period of seven weeks by a post test and a delayed test. The findings revealed that using L1 equivalents could no.....

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