The purpose of this paper is to explore the effect of online animated books in English reading class in Korean elementary school, and to investigate how those materials affect young ELL learners’ learning attitude towards reading in English, and what features play a key role in promoting a motivation and an interest in terms of utilizing online reading materials. Total four elementary ELL learners of low level of English proficiency in Korea participated in this study for 12 weeks. Through Summer English immersion program, participants were encouraged to experience an online animated book as a primary reading source, and read them as many times as they could. To answer the research questions, an ethnographic research was conducted with semi-conducted in-depth interviews, followed by researcher’s fieldnotes and memos. The findings show that online animated books helped students to have a positive attitude in reading materials written in English by stimulating their interest. In particular, the multimodal features of visualized animation, sound, and music were key factors which naturally made students immerged in reading activity.