This study examined the effect of integrating reading and writing on EFL learners’ writing ability, vocabulary usage and learners’ perceptions. The participants were 63 Korean EFL college students randomly assigned to two groups. As homework, the learners in Group A (reading-writing integrated group) carried out summarizing and vocabulary tasks after reading English story books whereas those in Group B (writing-focused group) completed writing and vocabulary tasks in the textbook. The treatment lasted for eight weeks in total, four weeks before and after the midterm exam. Data were elicited from a pretest and a posttest for quantitative analysis, and a questionnaire survey and in-depth interviews for qualitative analysis. The results showed that both approaches had positive influence on developing learners’ writing ability and vocabulary usage. However, Group A showed greater improvement with regard to writing performance than Group B, and the difference was statistically significant. Group A also showed more improvement in vocabulary usage than Group B, although the difference was not statistically significant. Moreover, the survey and interview results indicated that learners perceived connecting reading and writing using English story books was helpful for improving their writing ability as well as vocabulary usage, and they showed a positive attitude toward the reading-writing integrated instruction.