Selama satu bulan peneliti mengamati bahwa di kelas XI Social High, siswa kurang terlibat dalam proses pembelajaran di kelas. Peneliti memutuskan untuk menggunakan Blended learningdengan menggunakan media sosial berupa facebook untuk mengatasi masalah tersebut. Oleh karena itu, peneliti menerapkan Blended learninguntuk dapat meningkatkan keterlibatan siswa kelas XI Social High. Metode penelitian yang digunakan adalah metode Penelitian Tindakan Kelas (PTK) model spiral oleh Kemmis dan Taggart yang berlangsung selama dua siklus. Penelitian dilakukan pada 10 November sampai 17 November 2014 pada siswa yang berjumlah 24 orang dengan menggunakan beberapa instrumen antara lain lembar wawancara guru mentor, serta lembar observasi guru mentor yang mencakup lembar observasi keterlibatan siswa, lembar observasi penerapan fase Blended learningdan lembar umpan balik mentor, serta jurnal refleksi dari peneliti. Melalui penelitian tersebut, hasil penelitian menunjukkan bahwa penggunaan Blended learningmelalui media facebook dapat meningkatkan keterlibatan siswa yang ditunjukkan melalui tercapainya indikator keterlibatan siswa, antara lain siswa mengerjakan apa yang diminta oleh guru, siswa tidak melakukan hal-hal yang mengganggu pembelajaran, dan siswa juga terlibat untuk bertanya dan menjawab pertanyaan melalui penggunaan media sosial berupa facebook tersebut. Dengan menerapkan fase-fase Blended learningmaka dapat menunjang tercapainya keterlibatan siswa selama proses pembelajaran siswa di dalam kelas. / For one month, the investigator has been observing the Grade XI Social High students, and found that the students were not actively involved in the learning process. The investigator then decided to use Blended learningmethod through a social media namely Facebook to solve the problem. Therefore, the investigator applied Blended learningmethod in order to increase the Grade XI Social High students’ engagement. The research method that was used is Classroom Action Research, with a spiral model by Kemmis and McTaggart and two cycles were conducted. The observation was held on November 10 until November 17, 2014 on the 24 students by using some instruments such as mentor interview sheet and observation sheet that covers observation sheet for students’ engagement, observation sheet for the application for the implementation of Blended learningmethod and also mentor feedback sheet, and the investigator’s journal reflection. Based on the observation, the results explain that by using Blended learningthrough Facebook, the students’ engagement increased. It can be seen that the students did what the teacher instructed, they did not do disruptive behavior during the learning process and they also became active as they answered the teacher’s questions that were posted on the social media, Facbook. Applying the phases of Blended learningmethod can support the achievement of the students’ engagement during the learning process.