The study that we report in this paper, named as learning study, is a hybrid between a design experiment as characterized by Brown and Collins, and a Japanese lesson study as characterized by Yoshida, and Stigler and Hiebert. This paper aims at tracing the development of the learning study and examining its impact on teacher professional learning, through the example of an empirical study conducted in Hong Kong. First, the notion of learning study is explicated, together with the related ideas of the lesson study approach, the teaching research group and design experiments. Second, an empirical study is reported, which documents how a group of economics teachers in Hong Kong worked collaboratively within the learning study model to improve student learning, and in doing so enhanced their own professional learning. Finally, the implication of learning study for teacher professional learning is discussed. (Contains 2 tables and 2 notes.)