This article examines the influence of different reading conditions (i.e. reading only and reading with first language marginal glosses), number of word encounters (one, three, and seven) while reading, and combinations of these two variables on new word retention. This study considered a total of six possible combinations. Six groups of Chinese learners of English as a foreign language (EFL) (n = 240) were randomly selected and each assigned to a condition including 15 target lexical items. Each treatment session lasted for 5 weeks. One delayed test, containing four dimensions of vocabulary knowledge, was intended to measure learners' retention of unknown words. The delayed test was administered 2 weeks after the experiment and was not disclosed to the learners in advance. The groups whose reading was accompanied by first-language (L1) marginal glosses scored significantly higher than the reading-only groups. The increased effectiveness of repeatedly encountering target lexical items was more pronounced in the reading experiment including L1 marginal glosses. The combination of L1 marginal glosses and seven encounters was found to be the most effective combination for lexical item retention. This study highlighted the effectiveness of repeatedly encountering target words and being provided with L1 marginal glosses to retain new words incidentally learned from reading. The conditions and relevant teaching implications are discussed in this study.