The aim of this study was to explore the effects of post-reading group discussions in both first (L1) and second (L2) languages on L2 reading comprehension. The participants were fifteen Japanese university students of intermediate-level English. Three cohorts read four English texts and produced individual written recalls. Group 1 (the control group) responded in writing without discussion; group 2 discussed the texts in their L2 (English) before producing written recalls, and group 3 discussed the texts in their L1 (Japanese) before writing their recalls. The findings show that participants in the L1 discussion group used a larger number of higher-order processing and reading strategies than did those in the other two groups, suggesting that L1 group discussions have a positive effect on learners' reading comprehension. The authors make recommendations for teachers to use bilingual teaching strategies and to encourage the strategic use of the L1 in the L2 classroom.