This investigation was carried out to study the effect of temperature resulting from different planting dates during the stage of flowering and seed maturity and the effect of genotypes x environment interaction on seed 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 for each planting date. Three cuts were taken after 70, 110, 145 days from sowing. The experiments were conducted during 2014/2015 and 2015/2016 seasons in experimental farm of Assiut University. Results revealed that the highest number of seeds/ inflorescence (48.1), seed setting (72.8%), 1000 seed weight (3.21 g) and seed yield (1.25 kg/plot) were obtained from sowing on the 15^th September. This result due to seed production is taking place during the period from April to the Mid-June. The Sakha-4 variety outyielded (1.07 kg/plot) other tested varieties. On the other hand, the local variety gave lowest yield (0.90 kg/plot) over all planting dates and seasons. The estimates of genotypic stability parameters (a and l) for seed yield showed that variety Sakha-4 was the highest seed yielding, but exhibited less stability (instable) in seed yield. While Helally and Serw-1 varieties were more stable. On the other hand, local variety showed lower seed yield and instability.