The aim of this study is to analyze error cases induced during the proficiency test of certified odor measurement agencies. In the case of the homogeneity test performed in three panel groups, the geometric mean dilution factor of the site boundary PTMs(proficiency testing materials) was 1.4 ± 0.2, 1.7 ± 0.2, 1.8 ± 0.1 and that of the outlet PTMs was 3.7 ± 0.2, 3.7 ± 0.3, 3.7 ± 0.3, respectively. In the case of the stability test for 72 h, the geometric mean dilution factor of the site boundary PTMs was 1.6 ± 0.1 and that of the outlet PTMs was 3.6 ± 0.1. Among error cases induced during the proficiency test of certified odor measurement agencies, the proportion of error cases was in the order of case II(discontinuance of estimation)(40.0%) > case I(error on estimation procedure by panelist)(33.3%) > case III(miswriting of estimation result)(13.3%) > case IV(miswriting of dilution factor) and V(writing of wrong estimation result)(6.7%). Therefore, it seems likely that additional education related to error cases II and I is required. Keywords : Air dilution olfactory method, Proficiency test, Complex malodor, Certified agency