This research aims to develop a Natural Science Learning Material based on Guided Inquiry Model that is feasible to improve students’ critical thinking skill. The learning material is developed  using Dick and Carey model through a try out-design namely one group pre-test - post-test design. The lesson plans have been tried out to 12 students’ of IX-3 class at SMPN 3 Meulaboh in the second semester of 2016/2017 academic year in order to measure the aplicability of the lesson plans, learning obstacles, the result of students’ learning in from of critical thinking  students’ responses to the develoved lesson plans. Based on the data analysis, it can be concluded that the Science Learning Material based on guided inquiry model was feasible to improve students’ critical thinking skill.