This study investigated the impact of topic interest, alongside L2 proficiency and gender, on L2 vocabulary acquisition through reading. A repeated-measures design was used with 135 Korean EFL students. Control variables included topic familiarity, prior target-word knowledge, and target-word difficulty (word length, class, and concreteness). Participants read both high- and low-interest topic passages and took vocabulary posttests (word-form recognition, translation recognition, and translation production) immediately and four weeks after reading. Analyses revealed significant effects of topic interest and L2 proficiency, and a significant interaction between topic interest and gender. These results were maintained over time. The article concludes by discussing the facilitative role of topic interest, expanding on the motivational factor considered in the involvement load hypothesis.