This article describes the development and psychometric evaluation of behavioral belief, normative belief, and control belief scales, derived from the theory of planned behavior to predict physical activity intentions of persons at risk for diabetes. In Study 1, belief statements from interviews were categorized, ranked, and evaluated for item construction. Content validity was established by 96.1% agreement among a five-member expert panel. In Study 2, items developed from the belief statements were administered to 106 adults at risk for diabetes. Psychometric analyses provided evidence of construct validity and reliability of the three scales. Internal consistency was sufficient (α = .76-.95), and test-retest evaluations indicated scale stability (r = .79-.91). Factor analyses and confirmatory factor analysis using structural equation modeling provided evidence that the items were appropriately grouped under each construct. Researchers and practitioners can use these measures to assess behavioral, normative, and control beliefs about physical activity among persons at risk for diabetes.