This research aims to develop practical guideline of natural science that can improve critical thinking skills in junior high school students. Indicators of students' critical thinking skills include interpretation, analysis, evaluation and inference. This study was a Research and Development with Analysis method, Design, Development, Implementation and Evaluation (ADDIE). Validation associated with test format, content/material, and language was done by experts, while the implementation was given to 35 students in one of Junior High Schools in Jember. The instruments used are documentation, validation sheets, observation sheets, pretest and posttest. Written and lab test results showed an increase in students' critical thinking skills. Based on indicators of critical thinking skills Ngain value was 0.5, in which it was categorized as moderate. Practical guideline of natural science developed was considered as decent and quite effective in improving students' critical thinking skills. ABSTRAK Penelitian ini bertujuan mengembangkan petunjuk praktikum IPA yang valid dalam meningkatkan kemampuan berpikir kritis siswa SMP. Indikator kemampuan berpikir kritis siswa mencakup interprestasi, analisis, evaluasi dan inferensi. Penelitian ini merupakan penelitian Research and Development dengan metode Analysis, Design, Development, Implementation and Evaluation (ADDIE). Validasi ahli dilakukan dengan uji expert terkait dengan format, isi/materi, dan bahasa, sedangkan uji coba produk diberikan kepada 35 siswa di salah satu SMP di Jember. Instrumen yang digunakan adalah dokumentasi, lembar validasi, lembar observasi, pretest dan posttest. Hasil tes maupun praktikum menunjukkan adanya peningkatan kemampuan berpikir kritis siswa. Berdasarkan indikator kemampuan berpikir kritis diperoleh nilai rata-rata Ngain 0,5 dengan interpretasi sedang. Pengembangan petunjuk praktikum IPA yang dikembangkan dalam kategori layak sehingga cukup efektif dalam meningkatkan kemampuan berpikir kritis siswa.