Lesson plans are generally written in a way that helps teachers to layout and run classroom activities. Many researchers have examined how teachers go about planning. This clearly shows that instructional plans play a central role in teaching and creating effective learning environments (Clark & Dunn, 1991; Reiser & Dick, 1996; Shauelson, 1983 cited in Koszalka et al., 1999). In context of school using lesson study and open approach followed conception of Inprasitha (2010), the importance of lesson study processes is collaborative lesson planning. After that the teachers who participate in lesson study group use these lesson plans in the classroom, observe and collect students’ thought and learning processes. And in planning the lessons use problems that students encounter in everyday life, so as to stimulate students to work to achieve the objective (Fernandez & Yoshida, 2004). The data were collected by video and audio recording while the target group were planning and teaching the lessons in lesson study process, then were transcribed to the protocol and analyzed by using theoretical framework of Stigler and Hiebert (1999). The research revealed that the target group discussed during the lesson planning process detailing about exact words, problem situations, materials, the anticipated solutions, students’ thoughts and responses, time used in each part of the lesson, and how to summarize the lesson. In the lesson planning, the exact words used in the problem situations were mostly mentioned. Moreover, in lesson planning, the issue of details of introduction design was discussed a lot. There were some issues which were not discussed during the teachers-included designing of the lesson plan. However, they were discussed while the teacher was using the lesson plan in class during instructional management.