This study aimed to evaluate the economic viability of the performance of crossbred lambs (1/2 Santa Inês+ 1/2 Sulfolk), feedlot, fed different diets of hay Cynodon dactylon. The experiment was conducted at the agricultural sciences college, Federal University of Grande Dourados. Thirty non-castrated, crossbred Suffolk lambs were used, identified with ear tags, with an average age of 90 d, with average body weight (21.5 kg ± 1.61). The animals were blocked by weight and randomly assigned to one of the 6 hays. Hays of each cultivar (Jiggs, Vaquero, Tifton 68 Coast-cross, Tifton 85, and Russell) were harvested at 42 d of age or stage of maturity were fed as 60% of the diet with a standard concentrate making up 40% of the diet. The treatment diets were distributed in a fully randomized block with 5 replications. Means were analyzed as mixed models using the MIXED procedure of SAS software, 9.2 version, and the average compared by Scott Knot test at 5% probability. The intake of dry matter varied from 0.858 kg for Tifton 68 to 1.06 kg for Jiggs. There were significant differences between diets for total cost on feeding, and the Jiggs presented the highest values ($17.11/animal). The animals fed Tifton 68 hay showed higher net income ($41.84/ animal and $44.70), when the animal was sold for slaughter in the refrigerator or alive for rearing in contrast to the other treatments. The animals fed diets with hay Tifton 68 had a higher rate of return (2.16%) and profitability (34.63%) compared with the other diets. In conclusion, the use of Tifton 68 hay in diets of lambs in finishing stage, feedlot, brings higher economic returns compared with other diets containing Cynodon hay grasses.