This paper discusses the study of the effectiveness of the multimedia electronic English textbook for after-school programs in elementary schools developed by the Ministry of Education, Science and Technology (MEST) and Korea Institute for Curriculum and Evaluation (KICE). A total of 402 students in grades 3 through 6 and 117 teachers in the four research schools located in a metropolis, two small towns, and a rural area participated. Drawing upon the analysis of the multimedia textbook satisfaction survey and the T-test results of the English proficiency tests, the study demonstrated that the multimedia electronic English textbook benefited elementary school students` English learning in terms of both affective aspects and English proficiency. Both the elementary school students and teachers were greatly satisfied with the multimedia textbook. Concerning English proficiency development, the students improved their English proficiency after they used the textbook for one academic year; however, the students did not show considerable improvement in all the four language skills. This study suggests that the multimedia electronic English textbook would serve students` and teachers` needs for English instructional materials which encourage students` interactive and self-directed learning and improve their English proficiency.