Modified atmosphere technology consists in replacing the air inside the package by a mixture of gases (O2, CO2, N2) The increasing in foods shelf life is due to the antimicrobial activity of carbon dioxide. This study aimed to evaluate the effect of five gas mixtures with different concentrations of O2 and CO2 (A= 15% O2 + 85% CO2, B: 30% O2 + 70% CO2; C= 45% O2 + 55% CO2; D= 60% O2 + 40% CO2; E = Vacuum (control)) on microbial stability of lamb meat stored at 1 ° C ± 1 ° C. At intervals of three days, counts were performed for aerobic and anaerobic psychrotrophic microorganisms, lactic acid bacteria (LAB), thermotolerant coliforms (TC) and coagulase-positive staphylococci (CPS). The presence of Salmonella was also evaluated. TC, CPS and Salmonella were not found in all samples throughout the storage period. Regarding spoilage microorganisms, for LAB and anaerobic psychrotrophic no significant differences (P> 0.05) among treatments were found, and all samples reached the maximum limit of 107 CFU.g-1 on the eighteenth day of storage. For aerobic psychrotrophic counts, samples subjected to 15% O2 + 85% CO2 reached the maximum count after 18 days of storage, samples packaged under 60% O2 + 40% CO2 and vacuum on the eleventh day, and under 30% O2 + 70% CO2 and 45% O2 = C + 55% CO2 after 14 days. It is important to mention that the counts for all samples on the first day was already 104 CFU.g-1.This study showed that lamb loins subjected to modified atmosphere packaging with 15% O2 + 85% CO2 can be stored safely for 18 days under refrigeration. Longer periods may be obtained by avoiding contamination prior to packaging.