Background: Problem-based learning (PBL) has introduced as an important part of pharmacy education in Korea as it is effective method to help students gain and apply knowledge with development of problem-solving, critical-thinking, and decision-making skills. In order to provide the effective PBL, a number of trained facilitators and suitable PBL rooms are required. However, these become a barrier in Korea as most pharmacy schools have one or two faculty members who majored in clinical pharmacy. Objective: This study was performed to implement and evaluate a modified PBL in gastrointestinal (GI) pharmacotherapy class facilitated by one instructor. Methods: A general information of traditional PBL for 6 hours through 3 days is introduced before initiating GI pharmacotherapy class. After 3 hour-GI pharmacotherapy classes for 6 weeks, modified PBL was implemented with one instructor to facilitate PBL for four small groups with 19 pharmacy students simultaneously. Modified PBL was incorporated with weekly mini-case discussion and presentation. Results: Students completed 15-question survey to evaluate modified PBL course, student performance, group performance, and facilitator performance. Eighty-four percent of students answered modified PBL was helpful to understand what they have learned. Mean score in group performance was higher than that of individual performance during modified PBL course. Overall, students reported modified PBL was useful in knowledge building. Conclusion: Modified PBL model without individual group facilitators in one classroom helped students to achieve self-directed, independent learning skills in an interactive and engaging environment.