The main purpose of this paper is to investigate the contribution of the Lesson Study (LS) to the professional development of teachers. The present work, which is part of a broader research effort, was realized from February 12 to April 1, 2016 in the second grade of lyceum in a school in the prefecture of Attica. Initially, all the school's scholars (4) and 31 students participated. From the results of the survey, regarding the teachers' perceptions of the contribution of the lesson study to the differentiation of their attitudes and practices for the design of the course and their teaching, all the teacher participants in the research stated that they benefited from the lesson study as far as the subject of their teaching and the foresight of students' possible questions were concerned. At the same time, it has a positive impact on promoting co-operation and professional development of teachers as a form of training within the school.