The purpose of this study is to examine how reading motivation varies in its prediction of reading comprehension in Korean (L1) and English (L2) (with parental involvement being controlled for), and how reading motivation in each language is associated with language proficiency. Participants consisted of 289 EFL middle school students in South Korea. Three questionnaires and four language tests were employed to measure learners' reading motivation, parental involvement, language proficiency, and reading comprehension in their L1 and L2. Results indicated that L2 reading performance was positively predicted by both intrinsic motivation and grades/utility, whereas the only positive predictor of L1 reading comprehension was intrinsic motivation. Moreover, in both L1 and L2, the high-proficiency group was found to exhibit significantly stronger intrinsic and extrinsic motivation than the low group; the high group's intrinsic motivation was significantly stronger than the middle group; and the middle and low groups differed significantly in extrinsic motivation.