Recurrent otitis media are frequently intractable during childhood. It is unclear whether recurrent otitis media is caused by etiological bacteria colonization or by new infections. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were isolated from the nasopharynx of 7 otitisprone and 2 non-prone children with recurrent otitis media. Plural bacterial species and strains were found in all children while affected by otitis media. The same strain was repeatedly isolated from all otitisprone children even after administration of antibiotics but was not from the non-prone children. Antibiotic susceptibility did not differ significantly among the same repeatedly isolated strains. This pilot study suggests that the etiological bacteria tend to colonize and is hard to eliminate in otitis-prone children.