Soluble suppression of tumorigenicity 2 (sST2), a decoy receptor of interleukin-33 (IL-33), involved in allergic inflammation. Objectives: This study explored serum sST2 as a biomarker for disease activity and for predicting clinical response to sublingual immunotherapy (SLIT) in patients with house dust mite (HDM) induced AR. Methods: This study included 54 patients with moderate-to-severe AR (MSAR) and 54 healthy controls (HC). Serum sST2, total IgE, HDM-specific IgE, and eosinophil counts were measured. Serum levels of miR-223 were assayed using real-time PCR. Clinical severity was assessed using the total nasal symptom score (TNSS) and visual analogue scale (VAS). MSAR patients received SLIT for 6 months. Treatment response was defined by ≥30% reduction in symptom and medication scores.