Abstract. Feed is considered the most important factor affecting the composition of cow's milk of which the quality can be evaluated, essentially, through two parameters, the fat and protein content, because of their industrial interest. This study aims to evaluate the impact of seven different rations (R1-R7) on the protein and fat content of Prim’holstein cow milk in a cattle farm in Algiers. The results showed that the dry matter (DM) content of forages and concentrate was 72.74% (62.94% - 81.49%) and 27.25% (18.51% - 37.06%), respectively. The forage unit milk (FUM) and the digestible nitrogen matter (DNM) contents of forage were 60.50% (51.37% - 72.08%) and 61.15% (46.73% - 74.63%), respectively. In concentrate, the FUM and DNM contents were 39.50% (24.85 - 51.5%) and 38.85% (25.37 - 52.39%), respectively (Table 3). The forages showed significantly higher DM, FUM and DNM contents than the concentrate (p<0.0001). The type of ration showed a highly significant effect on the quantity of milk produced per day, protein content and defatted dry matter. However, no significant influence was observed for the fat content. The highest milk production (ranging from 17.31 to 19.64 liters/day) and the highest defatted dry matter (87.03 and 87.92 g/l) were recorded in cows which received rations R2, R3, R4 and R5 (p<0.0001). The highest protein content values (32.87 and 33.20 g/l) were observed in the milk of cows that were fed with rations R2, R3 and R4. The lowest levels were observed for rations R6 (31.80 g/l) and R7 (31.22 g/l) (p<0.0001). Protein to fat content ratio ranged from 0.79 to 0.84 and fat to protein content ratio ranged from 1.19 to 1.27. Good management of the diet and feeding practices of the dairy cows allow having an adequate protein and fat content in the milk. A diet composed of forages with an adequate supplementation in concentrate leads to the optimal results. Further studies are important to evaluate the effect of the physical form of the diet on the physicochemical quality of the milk.