Objective : This study was carried out to assess pulmonary function in ankylosing spondylitis (AS) patients. Methodology : Pulmonary function tests and integrative cardiopulmonary exercise testing (CPET) were studies in 20 AS patients and 20 healthy individuals. All subjects were also assessed for functional status with BASFI , measurement of chest expansion, lumbar spinal flexion with the modified Schober's method, and peripheral muscle function (assesed by measuring both muscle sterngth (Knee extensors ) and amount ( lean body mass ) . Results : The rypical respiratory function abnormalities in As were those of restricitve changes with decreased FVC. FEV1 . Vo2 max . and normal FEV1/ FVC. Pulmonary function showed correlations with chest expansion , lumbar stiffness as well as peripheral muscle function, Conclusion : This study showed that , in AS patients pulmonary function tests were defective and confirmed a restrictive type of impairment . Evaluation of pulmonary function and encouragement for more regular exercise to improve spinal mobility and muscle function should be given greater emphasis in ankylosing spondylitis patients.