Abstract： Objective To observe the bacterial biofilm in patients with chronic rhinosinusitis (CRS), and to investigate the possible relationship between biofilm and clinical factors. Methods Sixtynine patients with CRS ( study group), 15 patients with nasal septum deviation and 10 patients with nasal bone fracture (control group) were enrolled in the study. Mucosa specimens of uncinate process or ethmoid near the ostium of the maxillary sinus were obtained during endoscopic sinus surgery. The specimens were subjected to scanning electron microscopy. All patients were evaluated by questionnaire of chnical factors based on sino-nasal outcome test-20. SPSS 10. 0 was used for statistical analysis, and the relationship between bacterial biofilm and clinical factors was evaluated by Chi-square test. Results Bacterial biofilms were found in 49 patients ( 71.0％ ) with CRS. A marked destruction of the epithelium and cilia was observed in all samples of study group. No bacterial biofilm was found in the control group, and scanning electron microscopy showed normal epithelium and cilia in those specimens. Chi-square test showed that bacterial biofilm was not associated with clinical factors (gender, staging, course, nasal obstruction, phlegm, nasal discharge with stinking smell, headache, bloody nasal discharge and olfactory degeneration) in CRS. Conclusions Bacterial biofilms and destruction of the epithelium and cilia can be obscrved in CRS patients, which may be involved in the pathogenesis of CRS, but the formation of bacterial biofilm is not correlated with the clinical factors in CRS.