The objectives of this classroom action research are to improve the students’ writing skill by using mind mapping and describe the teaching and learning process when mind mapping is applied to teach writing. The problems which are faced by the students of the tenth grade of SMA Negeri 1 Boyolali in the academic year of 2012/2013 are the low level of the students’ writing skill and the students’ behavior in teaching and learning process. The procedure of the research consists of planning,implementing, observing, reflecting, and revising the action. The data are in the form of qualitative and quantitative data. The qualitative data were taken from the observation, the questionnaire, and interview with both the studentsand the teacher. The quantitative data were taken from tests conducted before and after implementing the action. The researcher got the students’ scores based on five writing indicators including content, organization, vocabulary, language use, and mechanic The research consists of two cycles. At the first cycle, the students were guided to practice writing using mind mapping in group. As a result, the students enjoyed group discussion because they could share their ideas in producing mind mapping but there were some students who did not involve actively in the activity. Although mind mapping improve the students’ writing score, it was not yet satisfying. The low scores were shown in two writing indicators: content and language use. The researcher conducted cycle two torevise the problems found in the first cycle. In this cycle, the students were guided individually during teaching and learning process. As a result, the students were more responsible for their activity. They improved each score of writing indicators and they passed the school passing grade. Based on the analysis of the data, mind mapping improves the students’ writing ability. It can be shown from the students’performance during the teaching and learning process. Mind mapping helps the students generate ideas and organize it into a good text. Mind mapping also helps the students check the use of grammar, vocabulary, and mechanic because the students are guided until they can arrange ideas into sentences. In addition, mind mapping increases the students’ participation during the teaching and learning process. However, there is weakness of mind mapping found in this research. The students enjoy generating ideas too much without considering which ideas are supporting ones and which are irrelevant. Therefore, it is suggested that this technique should be used with control attention and continues guidance from the teacher Penelitian ini bertujuan untuk meningkatkan kemampuan siswa dalam menulis dengan menggunakan mind mapping dan mendiskripsikan kegiatan belajar mengajar ketika mind mapping diterapkan untuk mengajar menulis. Permasalahan yang dihadapi oleh siswa kelas X SMA Negeri 1 Boyolali tahun ajaran 2012/2013 berkenaan dengan rendahnya kemampuan siswa dalam kemampuan menulis dan perilaku siswa selama kegiatan belajar mengajar. Jalannya penelitian terdiri dari perencanaan, penerapan, observasi, refleksi dan revisi kegiatan. Data yang digunakan dalam bentuk kualitatif dan kuantitatif. Data kualitatif diperoleh dari hasil observasi, kuesionair, dan wawancara guru pengampu dan siswa, sedangkan data kuantitatif diperoleh dari hasil pre-test dan post-test. Peneliti menilai test siswa menggunakan lima kriteria dalam menulis, yaitu isi, organisasi, kosa kata, tata bahasa, dan mekanik. Penelitian ini terdiri dari dua cycle. Cycle pertama, siswa dibimbing dalam diskusi grup untuk mengaplikasikan mind mapping dan sebagai hasilnya, siswa menyukai kegiatan diskusi grup tersebut karena mereka dapat berbagi ide-ide dalam membuat mind mapping, tetapi ada beberapa siswa yang tidak aktif didalam kegiatan diskusi. Peningkatan kemampuan menulis siswa denganmenggunakan mind mapping belum maksimal. Terdapat dua indikator dalam menulis yang masih di bawah kriteria ketuntasan manimal, yaitu isi dan tata bahasa. Berdasarkan hasil yang didapat pada cycle pertama, peneliti mengadakan cycle kedua untuk memperbaiki masalah yang timbul dalam cycle pertama. Dalam cycle pertama, siswa dibimbing secara mandiri. Sebagai hasilnya, siswa lebih bertanggung jawab terhadap kegiatan mereka selama proses pembelajaran. Peningkatan nilai siswa juga terlihat pada setiap indikator menulis. Berdasarkan analisis data, mind mapping telah meningkatkan kemampuan siswa dalam menuli. Hal ini dapat terlihat dari performa siswa saat kegiatan belajar mengajar berlangsung. Mind mappingmeningkatkan partisipasi siwa selama kegiatan pembelajaran. Mind mapping membantu siswa mengembangkan ide-ide dan menyusunnya menjadi sebuah teks yang baik. Mind mappingjuga membantu siswa dalam meneliti kembali penggunaan tata bahsa, pemilihan kata, dan mekanik karena siswa dibimbing sampai mereka dapat membuat kalimat berdasarkan ide-ide yang terdapat didalam mind mapping tersebut. Penerapan mind mapping mempunyai kelemahan, siswa terlalu senang mengembangkan ide-ide tanpa memperhatikan ide yang sesuai dan tidak sesuai dengan topik utama. Oleh karena itu, disarankan bahwa penerapan mind mappingharus disertai dengan bimbingan guru secara intensif