This study aims at investigating Korean high school students’ reading and writing relations in English with a focus on analysis of effects of reading journal writing which integrates reading and writing. Three groups (reading, writing, reading journal writing) had different treatments for 8 weeks. The results revealed that the reading journal writing group had the highest post-test writing scores compared with the two other groups. This group’s scores were statistically significant different from the reading group’s. The same results were also found in the higher-level group. As for the lower-level group, however, the scores of the writing group were highest. These results support the bidirectional hypothesis with a special emphasis on the interaction of reading and writing. The higher-level and the lower-level reading journal writing group had the highest post-test reading scores; however, no statistical significance was noted among the three groups. The results of the reading test do not seem to be clearly related to any hypothesis of reading-writing relations. The results of the questionnaire survey and interview and of the analysis of reading journal suggest that effects of reading journal writing can vary with reading texts and learners’ language proficiency level.