The dysregulation of microRNA (miRNA) expression contributes to the development of allergic rhinitis (AR). This study investigates serum miR-135a levels and their association with regulatory T cell (Treg) and T helper cell 17 (Th17) balance in AR patients. A total of 93 AR patients and 76 healthy controls were retrospectively recruited. Levels of serum miR-135a, peripheral blood Th17 and Treg cells, and Treg/Th17-related cytokines were measured. We assessed the diagnostic value of serum miR-135a for AR and its relationship with Treg/Th17 balance. AR patients showed significantly elevated immunoglobulin E (IgE), peripheral blood Th17 cells, and IL-17 and IL-6 levels, alongside reduced serum miR-135a, Treg cells, IL-10, TGF-beta 1, and Treg/Th17 ratios. A serum miR-135a of <= 0.536 demonstrated diagnostic potential for AR. Patients with higher serum miR-135a levels displayed increased Treg cell level and Treg/Th17 ratios, reduced Th17 cell, and lower total nasal symptom score (TNSS). Serum miR-135a levels in AR patients negatively correlated with TNSS, IL-17, IL-6, and Th17 cell percentages, and positively correlated with IL-10, TGF-beta 1, Treg cell percentages, and Treg/Th17 ratios. Collectively, decreased serum miR-135a levels in AR patients are associated with Treg/Th17 balance, supporting miR-135a as a potential biomarker for AR diagnosis.