In learning assessment research, few studies have directly compared cross-linguistic learning factors in the same group of students, and how these cross-linguistic factors affect language learning outcomes. In order to fill this research gap, we examined the similarities and differences in learning motivational factors and reading achievement among two-hundred sixty seven Chinese junior middle school students in Beijing. They were assessed on reading motivation inventories in Chinese as a first language (L1) and English as a foreign language (EFL), one Chinese reading test, and one EFL reading test. Analysis of variance on eight dimensions of reading motivation factors suggested that, students Chinese reading was outperformed significantly their EFL reading on self-efficacy, curiosity, involvement, recreation, and social-peer attitudes. Moreover, correlational results suggested that, instrumentalism was significantly correlated with EFL reading scores, whereas recreation was significantly associated with Chinese reading scores. Multiple regression analysis indicated that different dimensions of L1 and EFL reading motivation explained the variance to certain extent in L1 and EFL reading outcomes. The results emphasizes the important cross-linguistic feature of reading motivation in reading performance, and varied motivation strategies may play different roles in L1 and EFL reading. Suggestions on language reading instructions were discussed. （197 words）