Seasonal allergic rhinitis (SAR) is a global health issue, and the current standard of care (SoC) has limited effectiveness in controlling the disease. There is a need for innovative treatments to better manage uncontrolled SAR and advance beyond the uniform SoC, and biologics targeting type 2 inflammation driving allergic rhinitis is promising.To evaluate the efficacy and safety of Stapokibart, a humanized monoclonal antibody targeting interleukin-4 receptor subunit alpha, as an add-on therapy in patients with uncontrolled SAR.The PHECDA is a multicenter, randomized, double-blind, placebo-controlled, phase 3 clinical study designed to evaluate the efficacy and safety of Stapokibart in treating uncontrolled SAR in adults. Conducted across 18 centers in China during the pollen season, the study plans to recruit 108 adult patients with moderate to severe nasal symptoms despite receiving SoC during the previous seasonal pollen period, along with a 1-week run-in period and a baseline blood eosinophil count of at least 300 cells·μL-1. The study consists of a screening/run-in period (1 week), treatment period (4 weeks), and follow-up period (8 weeks). In addition to SoC, which includes mometasone furoate nasal spray and loratadine, participants are randomly assigned using a centralized interactive-web-response-system to receive either subcutaneous Stapokibart 600 (loading dose)-300 mg or a placebo every 2 weeks for 4 weeks. The primary endpoint of the study is the mean change from baseline in the daily reflective total nasal symptom score over the first 2 weeks of treatment. Subjects who have been administered at least 1 dose of the investigational drug will be included in the assessments of both efficacy and safety.This article outlines the methodology utilized in a multicenter trial studying Stapokibar for seasonal allergic rhinitis, with expectations to discuss its significant effects in subsequent analyses based on trial outcomes.The PHECDA study is for the first time to provide insight into the efficacy and safety of a seasonal add-on Stapokibart for patients with uncontrolled SAR during pollen exposure.NCT05908032.Copyright © 2025. Asia Pacific Association of Allergy, Asthma and Clinical Immunology.