The effects of heating on the aroma components of miso soup were investigated and are expressed by using odor-descriptive terms based on an evaluation of food odor. Aroma concentrates prepared from a heated and unheated miso suspension were analyzed by gas chromatography-olfactometry (GC-O) and GC-mass spectrometry. The GC-O analysis confirmed that the number of detectable aroma components in the concentrate prepared from the heated miso suspension was less than in that prepared from the unheated miso suspension. The flavor dilution factor evaluated by an aroma extract dilution analysis showed that 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H )-furanone contributed to the sweet aroma in the unheated miso suspension, while the mixed peak of methional and acetic acid contributed to the unpleasant aroma in the heated miso suspension most strongly.