The development and implementation of learning material on exposition text with a process for Senior High School (SHS) students on the teaching of Bahasa Indonesia is reported. The study is aimed to develop a learning material on exposition text with a process to be used as a learning media on the teaching of writing in Bahasa Indonesia. The study is carried out at state senior high school ("Sekolah Menengah Atas," SMA) Medan, Indonesia at academic year 2017/2018. The learning material is developed by enriching the topics with exposition text to meet the competence required by national curriculum in Indonesia. The learning material has been used as a media the teaching and learning activities in the experimental class and compared with ordinary book that has been used in control class on the teaching of Bahasa Indonesia. An excellent learning material has been obtained. Implementation of the learning material in the class has change students learning style moving from teacher centred to students centred learning. The developed material was found very effective as a learning media in the teaching and learning process and be able to improve students' achievement in Bahasa Indonesia. Students' achievements in experimental class (M=89.63±5.32) was higher than that obtained in control class (M=77.25±5.06). The students' writing skills are improved. Students performance in experimental class (M=86.04±6.89) was higher than that in control class (M=78.60±5.42). The learning facilities provided in the learning material are found to be effective to guide the students to improve their learning ability to write texts on exposition text with a process in Bahasa Indonesia.