Purpose: This study examines the reliability and validity of an Interprofessional Competency Assessment Scale for Undergraduates (ICASU) in the staged evaluation of an interprofessional education (IPE) program.　Participants: Participants were 355 undergraduates of Sapporo Medical University, department of nursing, occupational therapy, and physical therapy.　Data collection: We developed the interprofessional competency assessment form with 28 items, each using a 5-point Likert scale, to ask participants about their achievement and learning opportunities.　Analysis: Deleting items that showed ceiling effects in the achievement, we performed a factor analysis. Repeating the deletions till the factor loads of all items became 0.4 or higher, 16 items were selected for the ICASU. We conducted an exploratory factor analysis on achievement and learning opportunities. Using principal factor analysis and Promax rotation, we calculated the Cronbach alpha coefficient.　Results: We collected 314 (89.2%) valid responses. Factor analyses of ICASU data on achievement showed three factors: six items for ‘Basic communication skills’, four items for ‘Understanding one’s own and other occupations’, and six items for ‘Interprofessional collaboration skills’. Three similar factors were extracted on learning opportunities, showing agreement among all items except one. The α coefficients of the ICASU on the achievement and learning opportunities were 0.8 or higher.　Conclusion: The findings suggest that the ICASU is composed of three factors that indicate staged interprofessional competency in undergraduates and verify the validity of concepts and internal consistency. The usefulness of this scale in the staged evaluation of IPE needs to be explored.