Jurnal Pena Sains Vol. 5, No. 1, April 2018 p-ISSN: 2407-2311 e-ISSN: 2527-7634 THE DEVELOPING OF SIMPLE PROPS BASED ON GUIDED INQUIRY TO IMPROVE STUDENTS’ CRITICAL THINKING SKILL’S Desi Eka Nur Setyaningsih 1 and Astuti Wijayanti 2 1 Natural Science Education Study Program, Faculty of Teacher Training and Education University of Sarjanawiyata Tamansiswa Yogyakarta, 55165, Indonesia desiekanur@gmail.com 2 1 Natural Science Education Study Program, Faculty of Teacher Training and Education University of Sarjanawiyata Tamansiswa Yogyakarta, 55165, Indonesia astuti.wijayanti.@ustjogja.ac.id Abstract This research is aimed to 1) develop simple props based on guided inquiry. 2) know the implementation of simple props based on guided inquiry.3) know students’ critical thinking skill by using simple props. This research is research and development with 4D models. The average score in an aspect based on the whole result of the assessment by media expert is 99,33%, the material expert is 88,20%, peer reviewer 83,02%, and science teacher upon the simple props is 88,41%, then it can be stated as good. There is an improvement in the student’s result when doing pretest and posttest. The average score of the students when doing pretest is 5,29, and posttest is 7,9. The level of critical thinking skill of the students is on the level medium with the gain score is 0,54. Keywords: Critical thinking skill, Guided Inquiry, Simple Props