This study aims to identify effects of using online English storybooks on elementary school learners’ vocabulary ability and their affective domain. Eight English language learners who were 6th graders in elementary school participated in the study. They read 12 online English storybooks over 12 weeks. Before the experiment, the students took a pre-vocabulary test which tested some major words that would appear in the 12 storybooks and answered a questionnaire which tapped into the affective domain of the storybooks. The students also took a post-vocabulary test and a questionnaire at the end of the experiment. Additionally, individual interviews were conducted for an in-depth analysis, The results of this study are as follows: First, the online English storybooks had a positive effect on improving students’ vocabulary ability. All of the students’ scores improved in the post-vocabulary test, although two students did not make a high increase in their scores. Second, while reading the online English storybooks, students’vocabulary ability improved not only through implicit language learning, but also through explicit language learning. Third, using the online English storybooks had a positive impact on affective domain of most students. Finally, using the online English storybooks helped the students make self-learning habits.