<正>Objective: To study the composition of microecosystem in ostiomeatal complex （OMC） of adults and the changes via functional endoscopic sinus surgery. Methods: 220 adults with chronic sinusitis（20 as control） were classified into pre- and post-operative groups

and categorised according to its type of sinusitis. Swab specimens were taken from three different sites of ostiomeatal complex in each individual

and cultivations and identifications of aerobes

anaerobes and fungi were performed simultaneously. The microecosystem was analysed. Results: Cultured aerobes belonged to 30 species from 13 genera

anaerobes species

and fungi 3 major species

most of which have none or less virulence. The difference of mi-croecological status between type Ⅰ and Ⅱ was not significant （P > 0.05）. Aerobic culture rates between preoperative group and control group had significance（P < 0.01）;culture rate descended in postoperative group while the difference was not significant compared to preoperative group （P > 0. 05）; d