Abstract: Objective To assess the functional outcomes of patients undergoing total hip arthroplasty for ankylosing spondylitis (AS). Methods Between March, 2013 and May, 2016, 75 AS patients with ankylosed hip (involving 92 hips) underwent unilateral biological artificial total hip arthroplasty. The patients were followed up for 12-24 months and the changes in VAS score of the affected hip were evaluated. The changes in the range of motion (ROM) of hip, employment, BASFI and BASDAI score, and Harris score were analyzed after the operations. Results Significant improvements in general joint mobility, clinical symptoms and hip joint functions were achieved in all the patients. The average VAS score was significant reduced from 6.51± 1.32 preoperatively to 2.47 ± 0.38 after the operation. Significant improvements were also achieved after the operation in the average Harris hip score (from 22.51±3.32 to 89.17±2.52), the total ROM ( from 0 to 171.50±30.30), and mean BASFI score (from 6.2±2.6 to 2.3±1.2; all P<0.05). At the final follow up, 42 hips showed excellent outcomes, 38 hips had good outcomes, and 12 hips had acceptable outcomes, with a good outcome rate of 87%. By 6 and 12 months after the operation, 6 and 32 of the 75 patients returned to work. No neurovascular injuries, infections or dislocations was found in the patients during the follow-up; 1 patient had prosthesis loosening found by X-ray ordered for complaint of pain in the affected hip 4 months postoperatively. Five patients had heterotopic ossifications, including 3 grade Ⅰ hips and 2 grade Ⅱ hips according to the Brooker grading system. Conclusion Biological artificial total hip arthroplasty is effective for treatment of ankylosing spondylitis with hip stiffness with good functional outcomes of the hip joint.