The purpose of this article is to develop a design theory of blended learning curriculum in ways of establishing a model for designing such a curriculum and a model for designing an activity in a blended learning curriculum as well as demonstrating how these models can be utilized in a curriculum design. It first attempts to define what the essence of blended learning is by drawing on definitions of previous studies. Then, it goes on to identify the characteristics and rationales of blended learning. Finally, it exemplifies the devised BLC activity model, which is supported by the BLC design model and the BLC process model.