Background: Dupilumab exerts clinical effects, including improved sinus opacification, olfactory function, and quality of life, in patients with severe chronic rhinosinusitis with nasal polyps (CRSwNP). Meanwhile, only a few studies have reported its effects on nasal airway resistance and olfactory function, particularly in the Japanese population. Predictors of response remain unclear.Objective: In this prospective, observational study, we assessed the comprehensive efficacy and therapeutic response to dupilumab in severe CRSwNP patients with comorbid asthma.Methods: In 16 adult severe CRSwNP patients with comorbid asthma, the efficacy of 48-week dupilumab treatment, including olfactory function measured by a T&T olfactometer, nasal airway resistance measured by rhinomanometry, nasal polyp score, Lund-Mackay computed tomography score (LMS), and 22-item Sinonasal Outcome Test (SNOT-22), was assessed. Regarding asthma, the annualized rate of exacerbations, 7-item Asthma Control Questionnaire (ACQ-7), and spirometry were assessed. Treatment responsiveness was analyzed.Results: With 48-week dupilumab treatment, olfactory function, nasal airway resistance, nasal polyp score, LMS, and SNOT-22 scores improved significantly. Regarding comorbid asthma, the rate of exacerbations decreased, and ACQ-7 scores and lung function improved significantly. According to the European Position Paper on Rhinosinusitis and Nasal Polyps 2022/European Forum for Research and Education in Allergy and Airway Diseases criteria, 15 patients (94%) were moderate-to-excellent responders at 48 weeks of treatment. Patients with higher SNOT-22 scores, ACQ-7 scores, rates of asthma exacerbation in the previous year, and blood eosinophil counts benefited more from treatment.Conclusion: Dupilumab improved upper and lower airway outcomes especially in severe CRSwNP patients with comorbid, poorly controlled asthma.