Background Biofilms have given new insights to the understanding of pathogenesis of chronic rhinosinusitis (CRS). However, the link between biofilms. formation and local inflammatory response remains poorly defined in CRS with nasal polys. The aim of this study was to determine the potential association of the presence of biofilms in the nasal mucosal tissues with clinical features in Chinese patients, which had CRS with nasal polyps (CRSwNP). Methods A total of 19 patients with CRSwNP and 12 patients with non-CRS were subjected to endoscopic surgery and their nasal mucosal tissue specimens were examined histologically and by scanning electron microscopy (SEM). Their demographic and clinical features were recorded. Results Thirteen (68.4%) out of the 19 specimens from patients with CRSwNP, but none from control patients, were positive for biofilms that displayed typical characteristics of bacterial and fugal structures. The presence of biofilms in the nasal mucosal tissues was associated with significantly greater values of purulent nasal discharge and preoperative Lund-Kennedy scores, higher levels of serum total IgE and percentages of subjects with endoscopic surgery (ESS) history in patients with CRSwNP, and more severe inflammation in the nasal mucosal tissues of patients with CRSwNP. Conclusion Our study demonstrated the presence of biofilms in the nasal mucosal tissues of many patients, contributing to the understanding of the pathogenic process of CRSwNP in Chinese patients. Chin Med J 2012;125(6):1104-1109