Aim of the work: To analyze the serum levels of IL-33 in RA patients and to investigate its relation to the clinical characteristics, laboratory investigations, joint erosions, functional status and disease activity. Its relation to the presence of interstitial lung disease (ILD) was well thought-out. The study included 50 RA patients and 30 matched control. Thorough clinical examination, investigations, disease activity score (DAS-28) and health assessment questionnaire (HAQ) were considered in the patients. Bone erosion was evaluated and interstitial lung disease (ILD) was identified on high-resolution computed tomography. The serum level of IL-33 was measured by enzyme-linked immunosorbent assay. Results: Serum levels of IL-33 were significantly higher in RA patients (106.96 ± 52.6 pg/ml) than in healthy controls (46.9 ± 23 pg/ml) (p< 0.001). A significant correlation was found between IL-33 and the DAS28 (r= 0.4, p= 0.001), level of rheumatoid factor (r= 0.45, p= 0.001) and with the presence of ILD (r= 0.3, p= 0.04). There were no gender differences and the level did not significantly correlate with the age or disease duration. The medications received had no obvious effect on the IL-33 level. The level did not correlate with the HAQ. There was a significant correlation between the CT bone erosion scores the patient’s age, disease duration, rheumatoid nodules and DAS28. The erosion score also significantly correlated with the serum IL-33 levels in RA patients (r= 0.71, p= 0.001).