Teachers’ cognition and teachers’ beliefs are perceived to be a central issue in English language education in the recent decade. Therefore, there have been ample of study about teachers’ cognition and teachers’ beliefs either in ESL or EFL contexts. However, the research is mostly centred on the classroom pedagogical practices andlittle study has been reported about the issue outside the classroom practices. The present study, therefore,is aimed at getting a better understanding ofIndonesian EFL teachers’ cognition and beliefs about the new form of lesson plan (Rencana Pelaksanaan Pembelajaran / RPP)and its implementation in the classroom.  To achieve the goal, this study is grounded under the framework of qualitative case study. Two experienced EFL teachers at upper secondary schools were interviewed. The data generated from in-depth interviews were analysed using content analysis. The finding revealed that teachers’ cognition influenced the practical ways ofthe two teachers whendesigning and implementing the lesson plan, resulting plurality forms of the lesson plans. The second finding revealed that teachers’ beliefs about the lesson plan noticeablycontributed to diversity of teaching instructions and practices. The results of the study are expected to help shedding light on the new controversial lesson plan implemented under the 2013 Curriculum (Revised and Simplified Edition)