This investigation was carried out at Agronomy Department Farm, Faculty of Agriculture, Assiut University, Egypt, to study the effect of temperature resulting from different sowing dates, genotypes and their interaction on seed yield and its components of alfalfa. A set of ten genotypes namely; Ismailia-1, Nubaria-1, Ramah-1, populations from Forage researcher section (F.R.S.), Kharja, El-Dakhla, Farafra, Balady, Aswan, and Cuf 101, were subjected to five sowing dates (three autumns, i.e. October 10^th (D1), November 10^th (D2) and December 10^th (D3), and two springs  [March 20^th (D4) and April 20^th (D5)].