It was confirmed that malodor connected with an air-conditioner in an automobile is caused by microbial volatile organic compounds (MVOCs) produced by microorganisms getting into an air-conditioner when it is operating. Chemicals such as hydrogen sulfide, dimethyl sulfide, nbutyric acid, n-valeric acid, iso-valeric acid, n-octanol and toluene were detected above the odor threshold inside the automobile. The characteristics of a funky odor in the air blown into the automobile were due to detected sulfur compounds (hydrogen sulfide and dimethyl sulfide). Dimethyl sulfide was produced by microorganisms such as Aspergillus versicolor, Methylobacterium aquaticum, Herbaspirillum sp. and Acidovorax sp. In addition, the characteristics of a sour odor in the air blown into the automobile were due to detected organic acids (n-butyric acid, n-valeric acid and iso-valeric acid). N-valeric acid and iso-valeric acid were generated from Aspergillus versicolor, while iso-valeric acid was produced by Methylobacterium aquaticum. In addition, the odor intensity of the air blown into the automobile was affected by the concentration of detected sulfur compounds and organic acids. On the other hand, it is estimated that chemicals such as hydrogen sulfide, n-octanol and n-butyric acid detected in the air blown into the automobile were produced by non-identified species of microorganisms.