This study aims to develop the SIJAMET (Sijago Mathematics) application as a google sites-based learning media on material opportunities for class XI students that are valid, practical, and effective. This research is a research and development (research and development) with the ADDIE development model consisting of five stages: analysis, design, development, implementation, and evaluation. The data analysis techniques used are quantitative and qualitative analysis. The results showed that the validation of media experts obtained 83.33%, material experts 1 obtained 70.59%, and material experts 2 obtained 94.12%. The results of the teacher response questionnaire obtained 90.62%, and students obtained 88.52%. The results of the learning outcomes test obtained 90% of the completeness of learning. Thus the SIJAMET application has been valid, practical, and effective for students to use.Abstrak: Penelitian ini bertujuan mengembangkan aplikasi SIJAMET (Sijago Matematika) sebagai media pembelajaran berbasis google sites pada materi peluang untuk siswa kelas XI yang valid, praktis, dan efektif. Penelitian ini merupakan penelitian dan pengembangan (research and development) dengan model pengembangan ADDIE yang terdiri dari lima tahapan: analysis, design, development, implementation, and evaluation. Teknik analisis data yang digunakan adalah analisis kuantitatif dan kualitatif. Hasil penelitian menunjukkan bahwa validasi ahli media memperoleh 83,33%, ahli materi 1 memperoleh 70,59%, dan ahli materi 2 memperoleh 94,12%. Hasil angket respon guru memperoleh 90,62%, dan siswa memperoleh 88,52%. Hasil tes hasil belajar memperoleh 90% ketuntasan belajar. Dengan demikian aplikasi SIJAMET telah valid, praktis, dan efektif untuk digunakan siswa.