This study investigated the effects of explicit and implicit instruction on Korean university students' online processing of English transitive verb constructions in active and passive forms. Using eye-tracking methods, we explored cognitive processes in second language acquisition within an EFL context with limited authentic exposure. Participants were divided into two groups: one received explicit grammar instruction emphasizing direct teaching of grammatical rules, while the other experienced implicit instruction without focused grammar teaching. After 12 weeks, the explicit instruction group showed and retained significant improvements in processing, evidenced by increased gaze proportions on target images during the posttest. These learners demonstrated more focused and systematic gaze patterns, indicating deeper analytical processing due to the structured, rule-based instruction they received. In contrast, the implicit instruction group showed less pronounced improvements. These findings support cognitive theories suggesting that adult learners benefit from explicit, formfocused instruction due to their advanced metacognitive abilities. The study contributes to SLA research by confirming the efficacy of explicit grammar instruction, particularly in EFL settings like Korea, where classroom instruction is likely the only primary source of language exposure.