Medication-related osteonecrosis of the jaw (MRONJ) is a serious complication by antiresorptive medications and the treatment of MRONJ remains unclear. The present study developed a novel intraoperative infection-detecting liquid for MRONJ using various widely available and inexpensive dyes to detect infected bone areas. First, we performed a preliminary experiment using five dyes in a rat model of MRONJ. Eighteen female Sprague-Dawley (SD) rats were assigned to six dye groups: undyed, acid red, Brilliant Blue, phloxine, methylene blue, and Rose Bengal. Based on visual inspection and histological findings, Brilliant Blue and phloxine were selected for further evaluation. Next, twenty-eight SD rats were assigned to the control, undyed, Brilliant Blue, and phloxine groups and applied to experimentally induced MRONJ. The stained area was completely removed, and the bone defect was closed with sutures. Eight weeks after surgery, soft-tissue evaluation and histological and microcomputed tomography analyses were performed. The area of oral mucosal swelling was significantly smaller in the phloxine group than in the undyed and Brilliant Blue groups. The osteonecrosis area in the phloxine group was significantly smaller than that in the undyed group. These results suggest that phloxine staining is helpful for intraoperative differentiation of infected bone from normal bone.