The aim of this study was to explore teachers` values about teaching mathematics in the classrooms which implemented Lesson Study and Open Approach as a teaching approach. The targeted group was 83 school teachers from 4 schools participating in a teacher professional development project. The data was gathered through teacher questionnaires, lesson observations and interviews. Data analysis is based on Bishop`s (1988; 1996) and Komin`s (1990) frameworks. The results from the implementation of Lesson Study and Open Approach in Thai classroom found the different of the roles and behaviors of teachers and students in classroom. The results revealed 3 kinds of values about teaching: Mathematical values, General educational values, Mathematics educational values and also found that most of the teachers valued problem solving as an innovative teaching approach as against traditional approaches they were familiar with.