Penelitian ini bertujuan untuk mengembangkan instrumen penilaian proyek berbasis model discovery learning yang layak digunakan dan sebagai salah satu inovasi pengembangan penilaian proyek secara lebih oprasional. Penelitian ini merupakan penelitian pengembangan dengan mengintegrasikan model 4-D dengan model pengembangan instrumen non tes. Subjek uji coba yaitu peserta didik Kelas VIII SMP Muhammadiyah 3 Depok, Kabupaten Sleman. Data dalam penelitian ini diperoleh melalui: (1) penilaian berdasarkan masukan para ahli, untuk menentukan validitas isi instrumen; (2) hasil uji coba terbatas untuk menentukan reliabilitas instrumen, instrumen pengumpulan data berupa lembar observasi penilaian proyek untuk mengukur keterampilan pemecahan masalah. Instrumen penilaian proyek berbasis model discovery learning yang dikembangkan dinyatakan valid dan reliabel sehingga layak digunakan serta terbukti dapat digunakan untuk mengukur keterampilan pemecahan masalah peserta didik. Kata Kunci: penilaian proyek, keterampilan pemecahan masalah, discovery learning, pembelajaran IPA   Developing Discovery-Learning Based Natural Sciences Learning Project Assessment to Assess Problem Solving Skill   Abstract This research aims to develop project-based assessment instruments model discovery learning a proper use. This research is research development by integrating 4-D model with the model development of noninstrument test. The subject of the test i.e. learners Class VIII Junior High School of Muhammadiyah 3 Depok Sleman Regency. The data in this study were obtained through (1) assessment based on the input of experts, to determine the validity of the content of the instrument; (2) the limited Test Results to determine the reliability of the instrument, the instrument of data collection in the form of sheets of observation project assessment to measure problem-solving skills. The instruments of project-based assessment model of discovery learning developed declared valid and reliability so that the feasibility as well as proven can be used to measure student’s problem-solving skills. Keywords: project assessment, problem-solving skills, discovery learning, learning science