In capstone curriculums at the senior high school stage of technical high schools, capstone projects are required for students to produce the final product in the end of class. This study was designed to explore the effect of applying an inquiry-based learning (IBL) teaching strategy into capstone projects (CP-IBL) to promote students' inquiry ability and creative thinking. Students in two classes of a three-year major in electrical engineering participated.One class was assigned to an experimental group that was facilitated by a CP-IBL strategy emphasizing inquiry ability and creative thinking, while in the control group was taught with a traditional lecturing approach. There were seven stages used, including engagement, question, design, discussion, production, evaluation, and revision as the main framework for the experimental group, which was implemented in CP-IBL. Using a quasi-experimental research approach, ANCOVA analyses of abilities measures pre-and post-teaching showed inquiry ability and creative thinking of the experimental groups was significantly better than that of the control group.Keywords: inquiry-based learning (IBL), capstone project, quasi-experiment design, creative thinking ability, inquiry ability, IBL embedded in capstone project (CP-IBL) Several quantitative studies support the effectiveness of IBL as an instructional approach. Furtak, Seidel, Iverson, and Briggs (2012), for example, incorporated studies by using a broad range of terms to describe IBL (e.g., mastery learning and constructivist teaching); they reported an overall mean effect size of 0.50 in favor of the inquiry approach over traditional instruction. A meta-analysis by Alfieri, Brooks, Aldrich, and Tenenbaum