The lesson study (jugyoukenkyuu) approach to professional development, used in Japan and various regions of North America, encourages teachers to reflect on their teaching in order to improve its overall quality. The purpose of the current study is to analyze the influence of this approach on the professional development of English as a foreign language (EFL) preservice teachers in Turkey. The lesson study format was new to all participants, and data were collected from research lessons, observations, and reflections during the teaching process. The findings suggest that lesson study contributes to teacher learning by providing teachers with concrete examples of practice.