<p>This study examined effects of corpus-based instruction (CBI) on first-year undergraduates' receptive and productive vocabulary knowledge development and challenges. A mixed-methods approach and quasi-experimental design were used to answer the research questions. Participants of the study were 91 first-year undergraduate students aged over 18. Data were gathered through tests, reflective journals, and semi-structured interview. The one-way MANOVA results indicated a significant effect of both instructions on the participants’ receptive and productive vocabulary knowledge development. However, CBI had a medium to large effect size on the receptive vocabulary knowledge development and a small to medium effect on the productive vocabulary knowledge development. The reflective journal and interview data also showed that most of the participants found CBI easy. However, participants also pointed out that some concordance lines included difficult words to understand, and they were unable to access more than 20 words in 24&#xa0;h, which they saw as a challenge. Therefore, EFL teachers should integrate CBI to develop students’ receptive and productive vocabulary knowledge.</p>