Penelitian ini bertujuan untuk mengetahui bagaimana mengembangkan modul matematika serta efektifitasnya ditinjau dari kemampuan berpikir kritis matematis siswa. Subjek penelitian adalah siswa kelas VII SMP IT Bina Insani Metro. Penyusunan modul dilakukan berdasarkan panduan penyusunan modul dari Depdiknas 2008. Hasil validasi menunjukkan bahwa modul telah memenuhi standar kelayakan isi, media, dan bahasa. Hasil uji coba awal menunjukkan bahwa modul termasuk dalam kategori baik. Hasil uji terbatas dalam penelitian ini berupa modul matematika pada materi segitiga dan segi empat. Data penelitian diperoleh melalui tes berpikir kritis matematis. Hasil uji efektivitas menunjukkan siswa telah memenuhi kriteria ketuntasan minimal dalam kemampuan berpikir kritis matematis. Kata kunci: berpikir kritis, modul Abstract This research aimed to find out how to develop mathematics modules and its effectiveness in terms of critical thinking skills of mathematics. The subject of this research was students of VIIth grade of SMP IT Bina Insani Metro. The preparation of the module was done based on the guidelines on programming modules from Depdiknas, 2008. The result of validation indicate that the module has a standard feasibility of content, media, and languages. The results of the initial trials showed that the modules included in well category. The result of limited tests in this study was a math module on triangles and rectangles materials. The research data was obtained by the test of mathematical critical thinking. The results of effectiveness showed that students have completed a minimum standard in the ability of critical thinking of mathematics.