Modified mass selection method was used to study the gain from selection and compare between the base population and the half-sib families of alfalfa in 2016/2017 season. Selection was practiced among half-sib families for the best eight families (10% intensity of selection). Seeds of selected half-sib families and both modified mass selection cycles C1 and C2were evaluated for forage yield, some yield components and protein percentage. C1 significantly dominated over the base population as well as C2 significantly dominated the C1for plant height, leaf/stem ratio and forage yield. The realized gains after the two modified mass selection cycles were 6.89, 25.56, 15.87, 19.47 and 0.87% for plant height, leaf/stem ratio, fresh forage yield, dry forage yield, and protein percentage, respectively, over the base population. We may suggest from the results that modified mass selection resulted in a great improvement of forage yield, plant height and leaf/stem ratio, but in small gain for protein percentage. The values of genotypic coefficient of variation (GCV%) and phenotypic coefficient of variation(PCV%) were 5.28% and 7.03% for plant height, 1.30 and 1.79% for leaf/stem ratio, 7.76and 10.26% for fresh forage yield, 8.42 and 11.23% for dry forage yield and 5.53 and 6.55 % for protein percentage, respectively. Broad-sense heritability values for leaf/stem ratio and protein percentage were 72.94% and 71.25% which were higher than those for fresh and dry forage yields and plant height, at 56.47%, 57.07% and 56.15%, respectively.