Objective To study the incidence of postoperative delirium in elderly patients with mild cognitive impairment. Methods From June 2012 to August 2013, we recruited 64 elderly patients with normal cognition and 45 elderly patients with mild cognitive impairment undergoing hip fracture fixation. We tested the patients’ cognition at 1d, 2d and 3d postoperatively according to confusion assessment method (CAM) for diagnosis of postoperative delirium (POD). Results The incidence of POD in normal elderly patients was 12.5%, while the incidence in elderly patients with mild cognitive impairment was 31.1%. Conclusion The elderly patients with mild cognitive impairment have higher incidence of POD.