In this study we used grounded theory framework to explore how preparation for studying abroad affects the academic success of East Asian undergraduate students in U.S. universities. Based on interviews with 12 participants from China, Hong Kong, South Korea, and Taiwan, we found that knowledge of English language and American culture, which is closely involved with their preparation for study abroad and their undergraduate study in the United States, are two core categories affecting East Asian students' academic success. High levels of preparation for study abroad help East Asian students better adapt to American universities. At the same time, East Asian students spend more time on English proficiency tests than learning the culture both before and after they arrive to the United States, which can be detrimental. We suggest that U.S. universities provide more support for cultural adaptation such as learning communities to have active cultural exchanges within context.