BACKGROUND: The purpose of this exploratory study is to explain where, when and how the introduction of user fee system works in low and middle income countries using context, mechanism, and outcome configuration. METHODS: Considering advanced research in realist review approach, we made a review process including those following 4 steps. They are identifying the review question, initial theory and mechanism, searching and selecting primary studies, and extracting, analyzing, and synthesizing relevant data. RESULTS: User fee had a detrimental effect on medical utilization in low and middle income countries. Also previous and current interventions and community participation were critical context in user fee system. Those contexts were associated with intervention initiation and recognition and coping strategies. Such contexts and mechanisms were critical explanatory factors in medical utilization. CONCLUSION: User fee is a series of interventions that are fragile and dynamic. So the introduction of user fee system needs a comprehensive understanding of previous and new intervention, policy infrastructure, and other factors that can influence on medical utilization.