This action research evaluated the effectiveness of the Group Inquiry-Based Learning (IBL) Approach in teaching Land Traffic Law to Third-year English Teacher Trainees (Academic Year 2021-2022). The objectives were to study the approach's effectiveness and student satisfaction. The Sample comprised the total population of 11 3rd-year English teacher trainees (10 females) at Ban Keun Teacher Training College. The Research Instruments included a 20-item pre-test/post-test, a 21-item student satisfaction questionnaire, and a peer teaching observation form. Data Analysis employed Mean (x ̅), Standard Deviation (SD), and Percentage (P). The findings indicated that: Learning Achievement: The average post-test score was 18.36 (91.81%), confirming a significant improvement from the pre-test average of 15.54 (77.72%). Student Satisfaction: Overall satisfaction was High (x ̅=3.98). The lowest score was in Lesson content summary (x ̅=3.42), falling in the "Moderate" range. Teaching Quality: Observer assessments showed a high average of x ̅=4.35, demonstrating the approach successfully promoted group collaboration and planning. Conclusion: The Group IBL approach proved highly effective in improving student achievement and satisfaction in the Law subject, promoting significant learner progress.