This study investigates students’ perceptions of a writing-to-think, critical thinking (CT)-infused learning-log approach designed to support L2 learners’ reasoning and participation in English-medium classroom interaction at a Japanese university. Across seven oral communication classes (N = 182), students engaged in a write–speak–write cycle in which learning logs mediated pre- and post-discussion thinking by prompting learners to generate, clarify, and evaluate ideas through three recurring CTinfused tasks: opinion expression (OE), text interpretation (TI), and evaluation of viewpoints (EV). Quantitative results from a post-intervention survey indicated overall positive perceptions, with students reporting that log-writing helped them organize ideas, prepare for speaking, and participate more actively in discussions, although confidence in spontaneous oral expression remained comparatively lower. Thematic analysis of open-ended responses revealed three themes: (1) OE was perceived as the most effective task for clarifying ideas and building confidence; (2) writing before speaking supported participation by increasing clarity and easing speaking initiation; and (3) linguistic constraints, particularly limited vocabulary and difficulty verbalizing ideas, constrained fuller CT expression. Overall, CT-infused learning logs made students’ reasoning more visible while underscoring the need to strengthen L2 learners’ content-building and meaning-making skills to support fuller CT expression in interaction-focused learning environments.