We report a rare case of Mycoplasma hominis septic arthritis occurring simultaneously with acute gout. A Taiwanese native aboriginal presented with right ankle swelling, erythema, local tenderness, and limitation of range of motion after a vertebroplasty. He had a history of gout without regular follow-up. Under the polarized light microscopy examination, his synovial fluid revealed neutrophilic leukocytosis and monosodium urate crystals. Subsequently, 2 consecutive anaerobic synovial fluid cultures yielded a cell wall-free microorganism, which was identified as M. hominis based on polymerase chain reaction of its 16S rDNA. He did not defervesce under colchicine and indomethacin treatment until we prescribed a doxycycline and moxifloxacin regimen. He responded well to 6-week doxycycline and moxifloxacin treatment without bone destruction and loss of joint function.