This investigation was carried out to study the effect of temperature resulting from different planting dates during the stage of vegetative growth and the effect of genotypes x environment interaction on forage yield and its components in some varieties of berseem clover (Trifolium alexandrinum L.). A set of six varieties (Serw-1, Gemmeiza-1, Giza-6, Sakha-4, Helally and Local variety) were sown on four planting dates (September 15^th, October 15^th, November 15^th and December 15^th) in randomized complete block design with four replicates in experimental farm of Assiut University during 2014/2015 and 2015/2016 seasons. Three cuts were taken after 70, 110, 145 days from sowing. The results showed that the planting dates and varieties had a significant differences for plant height leaf/stem ratio, seasonal fresh and dry forage yields in both seasons and over the two seasons. Also, the tallest plant height was obtained from the plants sown on 15^th October in both seasons. Serw-1 variety significantly gave the tallest plant height over planting dates. Moreover, the highest leaf/stem ratio was obtained from the planting date at September 15^th in both seasons. Otherwise, leaf/stem ratio decreased gradually and reached to the minimum value at the December 15^th in both seasons. Local variety gave the highest leaf/stem ratio. The seasonal fresh forage yield significant decreased as planting date was delayed. Helally variety produced the highest seasonal fresh forage yield over the two seasons.  Meanwhile, the seasonal dry forage yield increased as planting date was delayed. No significant differences were noticed in seasonal dry forage yield among commercial varieties (Serw-1, Gemmeiza-1, Giza-6, Sakha-4 and Helally).  In the same the trend, the environments, varieties and their interaction were significant for plant height, leaf/stem ratio and seasonal dry forage yield. Finally, the stability analysis revealed that the average stability region involved Gemmeiza-1, Giza-6, Local variety and Serw-1 varieties for plant height, Gemmeiza-1, Local variety and Serw-1 varieties for leaf/stem ratio and Gemmeiza-1 and Helally varieties for seasonal dry forage yield.