Writing is one of the main academic skills that undergraduate students need in pursing their disciplines. Many researchers emphasize the importance of integrating reading with writing as the two skills involve similar cognitive processes. The current study aims to examine the effect of a an instructional program based on reading- writing integration on Jordanian undergraduate EFL students' writing performance and explore their attitudes concerning the effectiveness of the instructional program in developing their writing skill. To collect the data, three instruments were utilized: pre and post writing tests, a writing rubric and an interview. The study used a quasi-experimental design. The subjects of the study were 50 undergraduate EFL students from Philadelphia University in Jordan divided equally into a control group and an experimental group. The findings reveal that there is a significant differences at =0.05 between the two means of the two groups at the writing post-test due to the instructional program in favor of the experimental group. Furthermore, the instructional program has a positive effect not only on students’ overall writing performance, but also on the writing sub-skills: focus, development, organization and language. The program affected students' attitudes positively. Curriculum designers and instructors should integrate these two skills in the textbooks and teaching.