This study is related to the ozonation of free and combined amino acids, which present a high reactivity with ozone. Amino acids reactivities studied in the presence or absence of tert-butyl alcohol as radical scavenger were found to be related to their structures. Amino acid side chains seem to be the main sites that are responsible for the high ozone reactivity in polypeptide structures. Ozonation of amino acids led to the formation of aldehydes such as formaldehyde, acetaldehyde, glyoxal and glyoxal derivatives. The direct ozone reaction has been shown to favor aldehyde production.