Objectives: This study aims to investigate the feasibility and efficacy of competency-based course (Conceptual Geometry). In addition, this paper presents the procedures of developing competency-based course which include mapping out competencies of the course, developing a set of assessment instruments (e.g., diagonal, pre-and post-unit assessments, CBL comprehensive pre-and post-assessments). Methods: One hundred seventy-nine graduate students who enrolled in a 5-week Conceptual Geometry online course participated in this study. During the session, three sets of assessments were administered to assess the baseline of student knowledge (diagonal assessment), effectiveness (comprehensive pre-and post-assessments, and student content knowledge (5 sets of pre-and post-unit assessments). Results: The results of this study showed that implementing an online CBL course is feasible and effective at a course level. Students showed higher scores on all of the post-unit assessments (M = 95.45, SD = 4.62) than on the pre-unit assessments (M = 69.42, SD = 7.77). This result supports the increase of student knowledge associated with geometry contents and pedagogy. The post-comprehensive assessment results show an increase of student efficacy in geometry knowledge and skills using CBL course (pre-assessment: M = 4.49, SD = 0.86; and post-assessment: M = 5.14, SD = 0.40) which supports the increase of student efficacy of both content and pedagogical knowledge.