This investigation was carried out to study the effect of temperature resulting from different sowing dates, varieties and their interaction on forage yield and its components of alfalfa.  A set of seven varieties (Aswan, Balady, Dakhla, Ismailia-1, Nitrogen fixed, Genan, and Siwa) were sown on three sowing dates (20^th of October, November and December) in randomized complete block design with three replicates in experimental farm of South Valley University during 2014/2015 and 2015/2016 seasons. Three cuts were taken after 80, 125 and 165 days from sowing. The results showed that the sowing dates and varieties had a significant effects on plant height, number of branches/plant, leaf/stem ratio, fresh and protein forage yields over the two seasons. Aswan population gave the tallest plant height, and highest forage yields over all sowing dates. Moreover, the tallest plant heightm highest number of branches/plant and seasonal fresh, dry and protein forage yields were obtained from the plants sown on 20^th December over the two seasons. The sowing dates and varieties and their interactions were significant for plant height, number of branches/plant, and seasonal, fresh, dry and protein forage yields. Finally the stability analysis revealed that the average stability region involved Siwa, Balady, Dakhla and Nitrogen fixed populations for plant height and Genan and Ismailia populations for seasonal fresh forage yield. Moreover, all seven populations except Dakhla and Aswan populations were involved in stability region for seasonal protein forage yield.