Problem/Project-Based Learning (PBL) is a method of learning in which students solve problems or complete projects. To solve problems or complete projects, students work collaboratively in small groups. Through PBL, student motivation is expected to be enhanced, so this study investigated students’ motivational changes in PBL. Thirty-four undergraduate students who attended the PBL class were asked to complete questionnaires on 3 occasions; at the beginning, in the middle and at the end of the class. Questionnaires contained scales relating social motivation, and learning strategies. The results show that one dimension of social motivation (motive to be evaluated) increased in the process of PBL. The relationship of social motivation and learning strategies are discussed.