Purpose: Lesson study is a vital approach to improve teaching and learning that Japanese teachers have been utilizing for a century. Lesson study, however, has only recently been recognized as a teacher development strategy in Laos and started implementing in teacher training colleges (TTCs) in 2015. The purpose of this paper is to investigate the extent to which teachers have gained an understanding of the procedure of lesson study and to reveal their initial concerns about its implementation. Design/methodology/approach: This research reports on lesson study implementation in a Lao TTC during 2015-2017. Data were collected from 11 classroom observations, lesson study reports, lesson study guidelines, and 70 open-ended questionnaires. Findings: Data analysis revealed the initial experience of teachers in the suburb schools in applying lesson study to enhance teaching and students' learning outcomes, and their concerns regarding lesson study procedure including time management, the format of the lesson study report, and collaboration with lesson study facilitators. The importance of lesson study experts to facilitate the teachers' lesson study became clear. In addition, school principals and administrators have an important role in empowering teachers to engage confidently with lesson study. Originality/value: This study is the first trial project of school-based training for in-service teachers in a TTC and partner primary schools. The aim of the project is to strengthen and promote collaborative learning. To progress lesson study, it is very important to be sensitive to the teachers' issues in the early stages of the introduction of lesson study.