Medical students are expected to improve critical thinking, clinical reasoning and problem solving skills. These cognitive attributes need to be supported with metacognitive skills. Students with better metacognitive ability will be able to synergize their learning with self-reflection strategies to achieve learning target. One of the tools to assess students’ metacognitive skills is Metacognition Awareness Inventory (MAI). This study is aimed to validate Indonesian MAI in the academic stage of undergraduate medical education and was done on May-June 2014 at faculty of medicine Universitas Malahayati Bandar Lampung. This study used cross-sectional design consisted of 3 stages: language adaptation, pilot study and validation study. Validation study involved 1200 medical students. Factor analysis was conducted to identify factors of MAI. Language adaptation and pilot study produced Indonesian MAI which contains the same number of items. There were 757 MAI questionnaires eligible for analysis. Extraction of the 51-item MAI using principal component analysis (PCA) produced 5 factors which were cognitive preparation, supervision, management, strategy and evaluation. The Cronbach alpha value for the whole Indonesian MAI was 0.904. Indonesian MAI complies to construct validity criteria, specifically content validity and internal consistency. MAI is useful as an instrument to assess metacognitive ability in the academic stage of undergraduate medical education.