ABSTRAKPenelitian ini bertujuan untuk mendeskripsikan kelayakan dan karakteristik Lembar Kerja Peserta Didik (LKPD) berorientasi strategi REACT untuk melatihkan kemampuan problem solving siswa pada materi getaran harmonik di SMA. Penelitian ini merupakan penelitian dan pengembangan (R & D) dengan metode 4D yang telah dimodifikasi menjadi 3D dan terdiri dari tahap pendefinisian atau define, perancangan atau design, dan pengembangan atau develope. Tahap define terdiri dari hasil observasi, studi literatur, dan analisis kebutuhan. Tahap design pada penelitian ini yaitu pemilihan media dan materi perancangan, serta perancangan awal LKPD. Tahap develop dalam penelitian ini merupakan validasi ahli yang terdiri dari 4 orang ahli. Hasil dari validasi ahli dengan aspek kelayakan isi, bahasa, penyajian, dan kegrafisan yang dilakukan oleh validator rata-rata sebesar 95,96%. Karakteristik LKPD yang dikembangkan berupa Self instructional, Self contained, Stand alone, Adaptif, User friendly untuk melatih kemampuan Problem Solving berorientasi strategi REACT pada siswa SMA kelas X. Dengan demikian LKPD berorientasi strategi REACT pada materi getaran harmonik memenuhi kriteria sangat layak diujicobakan di SMA.Kata kunci: Lembar Kerja Peserta Didik, REACT, Problem Solving, Getaran HarmonikABSTRACTThis study aims to describe the eligibity and the Student Worksheet (LKPD) which is oriented towards the REACT strategy to practice the problem solving skills on harmonic vibration material in Senior High School. This research was a research and development (R & D) with the 4D method which has been converted into 3D and consisted of the stages of define, design, and develope. The define stage consisted of the results of observations, literature studies, and the needs analysis. The design stage in this research was media selection and material design, as well as the initial design of LKPD. The develop stage in this study is an expert validation consisting of 4 experts. The results of expert validation with aspects according to content, language, presentation, and graphics that carried out by validators were an average of 95.96%. The characteristics of the LKPD developed in the form of Self-instructional, Self-contained, Stand alone, Adaptive, User friendly to train Problem Solving skills oriented to the REACT strategy in the class X Senior High School students. Thus, the LKPD oriented to the REACT strategy on harmonic vibration material resulted the criteria very feasible to be tested in Senior High School.Keywords: Student Worksheet, REACT, Problem Solving, Harmonic Vibration