The paranasal sinusitis is one of the most common disease in the otorhinolaryngological field and its bacteriological study has been the subject of numerous investigators, but there have been many differences in the results of the studies. Authors performed aerobic and anaerobic culture to see the relation of the nature of retention fluid with types of lining mucosa in the maxillary sinus. The specimens were obtained from 60 sinuses that underwent Caldwell-Luc's operation from August 1982 to July 1983. Following results were obtained. The highest age incidence of patients who received Caldwell-Luc's operation was under 20 years of age in man and 21-30 years of age in female. Among 60 sinuses, bacteriae were isolated in 47 sinuses. Among isolated strains, Staphylococcus was the most common organism as 19 strains(41%), hemolytic Streptococcus 11 strains(23%) and Hemophilus influenza 6 strains(13%) in order. In bacteriological study related with the characteristics of retention fluid, Staphylococcus was more frequently encountered in cases of purulent retention fluid. In bacteriological study, related to the type of lining mucosa, there was no specific difference. Of the 42 sinuses that anaerobic cultures were performed, anaerobic bacteriae were isolated in 25 sinuses with relatively high incidence.