This research articulates a knowledge-building process in interaction-based e-learning. For exploration of a knowledge-building process, an interaction-based e-learning program was developed and implemented at a college level course. Throughout the course, quantitative and qualitative data including students' perceived knowledge-building process from questionnaires, online messages, interview data, and participatory observation journal were collected and analyzed. "s results, an observable action model and a conceptual model of the knowledge-building process were derived, which students and experts verified. Cognitive achievement factors and satisfaction factors were also considered in the knowledge building process model. Meaning and implication of each stage in the model were discussed.