A 77-year-old female with a 3-year history of left thigh pain and a diagnosis of hip osteoarthritis presented with worsening left thigh pain and the onset of lower abdominal pain and cold sweat. Computed tomography showed a left obturator hernia. The small bowel was not obstructed, and the obturator hernia was thought to contain the urinary bladder. Cystoscopy showed a recess in the left wall of the bladder, and cystography revealed protrusion of the bladder into the left obturator foramen. The patient was preoperatively diagnosed with obturator hernia of the bladder. Repair was performed using the midline preperitoneal approach. Within the obturator foramen, there was a hernia sac composed of thick peritoneum with the bladder lying along the medial wall of the sac. Intraoperative diagnosis was paraperitoneal bladder hernia through the obturator foramen. The obturator foramen was repaired with a polypropylene mesh, which was placed in the preperitoneal space and fixed to Cooperʼs ligament. We report a rare case of obturator hernia of the bladder treated by midline preperitoneal approach.