To evaluate the efficacy and safety of CLAVAMOX dry syrup (potassium clavulanate/amoxicillin) in children with otitis media, we conducted a postmarketing surveillance from February to September 2006. The analysis was made on the basis of 470 survey sheets collected from 127 medical institutions, of which we investigated 455 cases for safety, and 433 cases for efficacy. The efficacy was 95.2% in the 433 subjects eligible for the efficacy analysis. The clinical improvement rates for major symptoms (otalgia, otorrhea, flare reaction of drum membrane and fever) were 95% or more. The efficacies for the three major offending bacteria of otitis media (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis) were between 94.6% and 100%. The efficacies for penicillin-resistant Streptococcus pneumoniae (PRSP) and penicillin intermediate resistant Streptococcus pneumoniae (PISP) were 95% or more. Adverse drug reactions (ADRs) were reported in 106 (23.3%) of the 455 subjects eligible for safety analysis. The major ADRs were diarrhea, of which incident was 22.6% (103 of 455). These ADRs were observed at a higher rate in younger age patients. Most of the diarrhea cases were non-serious, reversible on discontinuation or continuation of the drug. No clinically important serious diarrhea cases such as pseudomembranous colitis or dehydration were observed. Our surveillance results demonstrated that CLAVAMOX dry syrup had excellent efficacy and clinically manageable safety in children with otitis media. These findings indicated that this medicine was clinically-useful in children with otitis media.