Research lessons, which take place within traditional Japanese lesson studies, have spread rapidly to many US schools since 1999. Lesson study is a form of teaching improvement that focuses on engaging in professional collaboration, peer observation, self-reflection, and critically discussing how to further enhance student learning. It provides the opportunity for teachers to learn about their own teaching as much a culture as a professional development activity. However, Japan and the US have vastly different educational systems. There are challenges in adapting Japanese Lesson Study for an American context. By the method of literature study, how lesson study can be adapted to be difficult in the United States are discussed. According to the challenges of lesson study in the United States, some suggestions on teachers' professional development in Taiwan are offered.