The aim of this study is to reveal the development of professional knowledge and competencies among pre-service English teachers through the practice of lesson study. This study was carried out to improve pre-service teachers' teaching skills and to show the effect of the practice of lesson study. The action research method was used in this research. Each action plan is a lesson plan and each lesson plan consists of two cycles. The study group of the research consisted of two pre-service English teachers from among fourth-year students studying in the English language teaching department of a public university and taking teaching practice courses in Turkey. In the research, interview, observation, reflective daily form, student evaluation form and the letter about the process were used as data collection tool. At the end of the research, it was concluded that the lesson study method improved the knowledge and usage skills of pre-service teachers' student-centered methods and technique and positively affected the pre-service teachers' views of the teaching profession and developed their beliefs about being successful teachers.