Objective To analyse the effect and its possible mechanism of modification of Kebi Tongluo Tang and Duhuo Jisheng Tang on treating ankylosing spondylitis（ AS） patients with liver and kidney Yin Deficiency pattern.Methods One hundred and eight AS patients were randomly divided into a control group and a treatment group

with54 cases in each group. The control group was treated with oral administration of indomethacin entric-coated tablets after a meal

50 mg per time

trice per day for 6 months

and the treatment group was given modification of Kebi Tongluo Tang and Duhuo Jisheng Tang

one dose daily

half in the morning and half in the evening for 6 months.The changes of physical signs and bone metabolism were observed before and after treatments

and the efficacy and security were also evaluated. Results The total effective rate in the treatment group was 90. 57%

showed no obviously difference compared with 78. 85% in the control group（ P > 0. 05）. Compared with pre-treatment

the physical signs indexes including the pillow-wall distance

finger-floor distance

jaw-handle distance

the mobility of the thoracic

lumbar vertebra and spine

and the Gaenslen test were significantly improved in both groups（ P <0. 01）

and the treatment group showed more improved than the control group（ P < 0. 01）. Meanwhile

the bone gla protein（ BGP） of patients were much increased and the parathyroid hormone（ PTH） were markedly descend in both groups（ P < 0. 05）

especially BGP in the treatment group（ P < 0. 05）. There is no significant difference in the adverse event rate between the treatment group（7. 55%） and the control group（3. 85%）（ P > 0. 05）. Conclusion The modification of Kebi Tongluo Tang and Duhuo Jisheng Tang had good efficiency in treating AS

and its mechanism might be related with regulating the hormones associated with the bone metabolism.