This work aimed to assess the impact of a diet based on green pastures of steppe rangelands and another based on a concentrate diet, on the composition of the intramuscular lipid fraction of different sections of the biceps femoral muscle of lambs, in two regions of the wilaya of Tiaret, in winter and in spring. The biceps femoral muscle sample collection came from 20 different lamb carcasses (10 samples for each of our two study regions, with 05 samples for each season). These samples were taken on different occasions in large butcher shops. Total SFA content in both regions shows dominance in lambs from the regimen concentrate, that C 16: 0 and C 18: 0 are the most dominant. There is no remarkable difference in total MUFA content, and on individual monounsaturated FA, between the two regimens. In both regions, the most dominant FAs in the intramuscular lipid fraction of pasture lambs are C18: 3n3 followed by C18: 2n6 cis-9, C20: 4n6, C20: 5n3, and C22: 6n3, compared to those from concentrate regimen; however, lambs from Chehaima concentrate regimen had the most dominant FA in their intramuscular fat, C18: 3n6 followed by C20: 4n6, compared to those from pastures of Naima. The values of the ratio n-6 / n-3 correspond to the nutritional recommendations. The feed ratio ΣPUFA / ΣSFA of lambs from pastures in the Chehaima region is the only one that corresponds to the desired value. Based on this research, it is concluded that lambs that have grazed grass in steppe rangelands have the richest meat in omega 3, which is more desirable and benefits for human health.