Supplemental Digital Content is Available in the Text. Objectives: To examine the effects of lumbopelvic stabilization exercises (LSE) and pelvic compression belts on muscle behavior in women with sacroiliac joint. Study Design: Feasibility randomized clinical trial. Background: Patients with unilateral lumbopelvic pain have been shown to have altered muscle recruitment patterns of the transverse abdominis (TrA) and internal oblique muscles. The effects of LSE and pelvic compression belts on muscle behavior are unknown in this population. Methods and Measures: Twenty-five women with unilateral sacroiliac joint pain were randomly assigned to the LSE plus belt (LSE + belt) group or the LSE group. Both groups received the same LSE for 12 weeks with the first 4 weeks under supervision. The LSE + belt group also received a pelvic compression belt for the first 4 weeks. Outcome measures, including the Modified Oswestry Low Back Pain Disability Questionnaire, Numeric Pain Rating Scale, and percent change of muscle thickness for the TrA and internal oblique, were collected at baseline, 4 weeks, and 12 weeks. In addition, Global Rating of Change Scale scores were collected at 4 and 12 weeks. Results: The analysis of variance results revealed no significant interaction for Modified Oswestry Low Back Pain Disability Questionnaire, Numeric Pain Rating Scale, or percent change of TrA and internal oblique; however, all had significant improvements in over time. There was no significant difference in Global Rating of Change Scale scores between groups. Conclusion: The results of this feasibility study did not offer clear evidence of the benefit of pelvic compression belt over LSE for those with sacroiliac joint pain. All participants demonstrated an increased muscle thickness of TrA in the first 4 weeks. [ABSTRACT FROM AUTHOR]