The effect of modified atmosphere packaging (MAP) with unconventional gas mixtures on the main qualitative parameters of sardine fillets during refrigerated storage was investigated. Four different atmospheres conditions were tested: air; 30% CO + 70% N; 30% CO + 70% NO and 30% CO + 70% Ar. All samples were packaged in polypropylene trays sealed with a high barrier film and stored at 2-4 °C for 12 days. The quality and the freshness of sardine fillets packed in MAP were evaluated by microbiological, physical and chemical analyses after 0, 1, 2, 5, 6, 8 and 12 days of the storage period. The 2-thiobarbituric acid-reactive substances (TBARS) values for MAP samples were lower compared to air samples, reaching a final value of 1.09 mg malonaldehyde (MA)/kg and 3.39 mg MA/kg, respectively. The samples packed in Ar reached the fixed threshold for total mesophilic and psychrotrophic bacteria after 12 days of storage, resulting the best MAP condition adopted, able to increase the sardine shelf-life of 3 days with respect to the other tested conditions. Air packed samples showed significantly higher (p < 0.05) Hx content (50 mg/kg) compared to the rest of the MAP samples (20 mg/kg). At the end of the storage period, the sample packed in Ar showed a significantly lower value (p < 0.05) (around 40 mg/kg), than the other MAP conditions.