The aims of this research is to determine the feasibility of the learning materials of Sciences with guided inquiry model to instruct student’s critical thinking skills. This research and development used Tessmer method to produce a prototype which was tested up to field test. The feasibility of learning materials is expressed by the validity, practicality, and effectivenees. The validity of learning materials is determined by expert and one to one test. The practicality is determined by the implementation of lesson plan (RPP). The effectiveness is determined by the ability of students to implementing LKPD. The result showed that; (1) the learning materials is valid according to the result of evaluation by expert and one to one test, (2) the learning materials is practically according to the result of implementation of lesson plan is 3,5, and (3) the learning matrials is effective according to the result of implementation of LKPD. Based of descriptive analysis it could be concluded that the learning materials developed are feasible and were able to instruct critical thinking skills of junior high school student. Keywords: learning materials, guided inquiry, critical thinking skillsAbstrakPenelitian ini bertujuan untuk mengetahui kelayakan perangkat pembelajaran IPA model inkuiri terbimbing untuk melatihkan keterampilan berpikir kritis peserta didik. Pengembangan perangkat dilakukan berdasarkan model penelitian pengembangan Tessmer sehingga menghasilkan prototype yang diujikan hingga tahap uji lapangan. Kelayakan perangkat pembelajaran dinyatakan dari kevalidan, kepraktisan, dan keefektifan. Kevalidan perangkat pembelajaran ditentukan dari hasil validasi oleh pakar dan hasil uji coba perorangan. Kepraktisan ditentukan dari keterlaksanaan RPP. Keefektifan ditentukan dari kemampuan peserta didik dalam melaksanakan LKPD. Hasil penelitian menunjukkan bahwa; (1) perangkat pembelajaran dinyatakan sangat valid berdasarkan hasil penilaian pakar dan uji perorangan, (2) perangkat pembelajaran dinyatakan praktis berdasarkan hasil penilaian keterlaksanaan RPP mencapai skor 3,5, dan (3) perangkat pembelajaran dinyatakan efektif berdasarkan kemampuan peserta didik melaksanakan LKPD. Berdasarkan hasil analisis deskriptif disimpulkan bahwa perangkat pembelajaran yang dikembangkan dinyatakan layak dan mampu melatihkan keterampilan berpikir kritis peserta didik.Kata kunci: perangkat pembelajaran, inkuiri terbimbing, keterampilan berpikir kritis