Serum amyloid A protein A (SAA) is a normal serum protein (serving as a precursor of fibrillar tissue protein AA), synthesized in the liver and a rapidly responding marker of the acute phase of inflammation. A constant high concentration of SAA is one of the factors in the development of AA-amyloidosis. As a rule, secondary amyloidosis develops in patients with long-term and poorly controlled inflammatory diseases, including rheumatic diseases, one of which is ankylosing spondylitis (AS).Objective: to assess the level of SAA in AS patients and its relationship with indicators of disease activity.Patients and methods. The study included 124 patients with AS who met the modified New York 1984 criteria. The disease activity and functional status of patients were assessed according to the recommendations of Russian experts. SAA and CRP, ESR in blood serum were measured in all patients.Results and discussion. The median SAA concentration was 12.5 mg/L [4; 71.6]. Of 124 patients, 31% had SAA levels 5 mg/L. A strong correlation was found between the levels of SAA and CRP (r=0.80, pConclusion. A statistically significant relationship was found between SAA and CRP levels, as well as the AS activity indices. Research has shown that SAA can be used as one of the markers of inflammation in AS.