Abstract As one of the foundations in the development of technology, physics must be supported by experimental activities that are able to develop a scientist's skills, such as scientific reasoning skills. Experiments with cookbook methods that have been conducted in various experimental activities are considered not able to maximize the potential of students because it does not provide wide opportunities for students to explore. One of the solutions to develop the scientific reasoning skills of physics students is the problem solving-based experiment approach. The research was conducted by one group pretest-posstest design to 20 physics students as research sample. The research instrument used is the scientific reasoning instrument test developed by Lawson which is known as Lawson Classroom Test of Scientific Reasoning (LCTSR) and student work sheet instrument (LKM) containing problems in daily life and questions about: tools and materials, prediction, exploration, measurement, analysis and conclusions. The results show all aspects of scientific reasoning being measured, i.e. 1) conservation of matter and volume, 2) proportional thinking, 3) identification and control of variables, 4) probabilistic thinking, 5) correlative thinking, and 6) hypothetic-deductive thinking has increased. Based on the result of research can be concluded that the problem solving-based experiment can improve the scientific reasoning skills of physics students. Keywords: Problem solving, experiment, scientific reasoning skills Abstrak Fisika sebagai salah satu pondasi ilmu dalam perkembangan teknologi harus didukung dengan kegiatan eksperimen yang mampu menumbuhkembangkan keterampilan seorang ilmuwan, diantaranya keterampilan penalaran ilmiah dalam menyikapi fenomena alam. Eksperimen dengan metode cookbook yang selama ini menjamur dalam berbagai kegiatan eksperimen dipandang tidak mampu memaksimalkan potensi mahasiswa karena tidak memberikan kesempatan yang luas kepada mahasiswa untuk bereksplorasi. Salah satu solusi yang dapat menumbuhkembangkan keterampilan penalaran ilmiah mahasiswa fisika dalam bereksperimen ialah pendekatan problem solving-based experiment. Penelitian dilakukan dengan desain one group pretes-postes design kepada 20 mahasiswa fisika sebagai sampel penelitian. Instrumen penelitian yang digunakan ialah instrumen tes penalaran ilmiah yang dikembangkan oleh Lawson yang dikenal dengan nama Lawson Classroom Test of Scientific Reasoning (LCTSR) dan instrumen lembar kerja mahasiswa (LKM) berisi permasalahan dalam kehidupan sehari-hari dan pertanyaan arahan mengenai: alat dan bahan, prediksi, eksplorasi, pengukuran, analisis dan kesimpulan. Hasil penelitian menunjukkan semua aspek penalaran ilmiah yang diukur, yaitu 1) kemampuan konservasi materi dan volume, 2) berpikir proporsional, 3) identifikasi dan kontrol variabel, 4) berpikir probabilistik, 5) berpikir korelatif, dan 6) berpikir hipotetik-deduktif mengalami peningkatan, sehingga dapat disimpulkan bahwa problem solving-based experiment mampu meningkatkan keterampilan penalaran ilmiah mahasiswa fisika. Kata-kata Kunci: problem solving, eksperimen, penalaran ilmiah