Objectives: The aim of this study was to investigate whether the prevalence of group 2 innate lymphoid cells (ILC2s) in sinonasal tissues or in peripheral blood is associated with the postoperative outcome in chronic rhinosinusitis (CRS) patients. Design: A cross-sectional study of CRS patients undergoing endoscopic sinus surgery (ESS). Setting: The Department of Otorhinolaryngology-Head and Neck Surgery at Shiga University of Medical Science Hospital. Participants: Eleven patients with eosinophilic CRS (eCRS) and ten patients with non-eCRS were recruited. Main outcome measures: We examined the ILC2 prevalence in sinonasal tissues and in peripheral blood before and after ESS. Lund-Mackay computed tomography (LMK-CT) scores were used to evaluate the postoperative outcomes; cases with more than 50% improvement were categorized into the good outcome group, and cases with less than 50% improvement were categorized into the poor outcome group. Results: The ILC2 prevalence in sinonasal tissues was correlated with that in preoperative blood in the eCRS and non-eCRS patients. The ILC2 prevalence in sinonasal tissues and in preoperative blood was not correlated with the pre- or postoperative LMK-CT scores. Postoperatively, the ILC2 prevalence in blood was decreased in the eCRS and non-eCRS patients, and the decrease was associated with the good outcome group, but not the poor outcome group. Conclusion: The decreased ILC2 prevalence in blood may be related to good postoperative outcomes after ESS in eCRS and non-eCRS patients.