Background: Ankylosing spondylitis (AS) represents a chronic, progressively inflammatory condition characterized by persistent inflammation, bone erosion, and development of syndesmophytes. The mechanism behind AS development has been the subject of various investigations. However, the involvement of interleukin-33 (IL-33) in AS has not been fully addressed. Objectives: The aim of this work was to assess serum IL-33 in AS patients versus controls, and elucidate its correlation with AS activity, function, sacroiliitis, enthesitis, and other AS disease indices.    Patients and Methods: Thirty patients diagnosed with AS had been included in this study, matched by age and sex to thirty healthy individuals. For all patients, assessment of sacroiliitis, peripheral arthritis, enthesitis, and assessment of different AS indices were done. IL-33 levels were measured in serum of both patients and controls. Results: Serum IL-33 appeared to be significantly increased in AS patients (380.7 ± 296.8 pg/ml) compared to controls (45.2 ± 28.11 pg/ml) (p < 0.001).  Active AS patients exhibited markedly elevated IL-33 levels (678.1 ± 312.3 pg/ml) compared to their inactive counterparts (208.4 ± 49.3 pg/ml). IL-33 demonstrated a robust positive correlation with disease activity, yet showed no association with arthritis, sacroiliitis, or enthesitis. Conclusions: Serum Il-33 was significantly higher in AS patients than control group. Serum IL-33 levels showed statistically significant correlations with AS disease activity, while displaying no discernible correlations with enthesitis, sacroiliitis, or peripheral arthritis. This could make it possible to include serum IL-33 as a part in the core set evaluation of AS disease activity.