Abstract: Background and Objective: Acetaldehyde is an inhibitor of growth of fungi including Alternaria alternata and alters biochemical processes. However, its effect on the regulation of the production of amino acids in A. alternata remained unknown. This study aimed to investigate the inhibition and co-regulation of five amino acids produced in Alternaria alternata exposed to acetaldehyde. Materials and Methods: To assess the regulation of the production of amino acids in A. alternata exposed to acetaldehyde colonies of this fungus were exposed this volatile compound at concentrations of 0, 5 and 10% over 24, 48, 96 and 120 h. Results: Results showed that acetaldehyde inhibited A. alternata mycelial growth in a dose-dependent manner. Moreover, evidence of suppression and co-regulation of the production of amino acids, leucine, isoleucine, proline, tyrosine and valine was discovered. Conclusion: From these results it could be concluded that acetaldehyde can suppress and co-regulate the production of the five amino acids.