This study aimed to empirically test the direct relationship between the constructivist learning environment and critical thinking ability and the indirect relationship between them when mediated by motivational beliefs and cognitive strategies. Responses from questionnaires were collected from a convenience sample of 967 students studying Liberal Studies or Integrated Humanities in Secondary Three (Grade nine) in Hong Kong. Analyzed by structural equation modeling, both cognitive strategies and goal orientations fully mediated the relationships between the constructivist learning environment and critical thinking ability. The finalized model showed an acceptable fit to the data and that 22% of the variance in critical thinking ability was explained, suggesting the usefulness of the model in predicting critical thinking ability.