This paper reports on the effect of carbon dioxide concentration on the formation of biogenic amines (BAs) in shredded cooked chicken breast fillet packed in modified atmosphere stored at 4C. The samples were grouped as follows: T1 (packed under atmospheric air), T2 (vacuum packaged), T3, T4, T5, T6 and T7 (packaged under modified atmosphere with 10, 30, 50, 70 and 90% CO2, respectively, and total volume completed with N2). Total viable count (TVC) and BA (tyramine, putrescine, cadaverine and spermidine) content were determined for 28 days. The results showed a gradual reduction in the growth rate of TVC as the concentration of CO2 increased. Also, in treatments with high CO2 contents, averaged concentrations of BAs detected were significantly smaller. In addition, increasing the concentration of CO2 caused a reduction in the amount of putrescine and cadaverine produced by bacteria. Amine quantification proved to be an adequate parameter to evaluate the quality index of this matrix. Practical Applications: Biogenic amines (BAs) are toxic low-molecular-weight organic bases and are mainly produced by microbial decarboxylation of amino acids. They are frequently found in high concentrations in food and cannot be reduced by high-temperature treatments; modified atmosphere is an alternative technology for their reduction. The consumption of food containing large amounts of BAs can result in allergic reactions, characterized by difficulties in breathing, rash and hypertension. In consequence, it becomes important to monitor the levels of BAs in foods because of its relationship to public health and food safety.