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 forage yield and its components of alfalfa. A set of ten genotypes (Ismailia-1, Nubaria-1, Ramah-1, populations from F.R.S., Kharja, El-Dahlia, Farafra, Balady and Aswan and Cuf 101) were sown on five sowing dates (three at autumn, October 10^th (D1), November 10^th (D2), December 10^th (D3), beside two at spring i.e. March 20^th (D4), April 20^th (D5). Two experiments were carried out as experiment I (2017-2019) and experiment II (2018-2020). Each experiment included all autumn and spring sowing dates. The split block design with three replications was used in both experiments. Fifteen cuts were taken in the two years from each sowing date for each experiment. The results showed that the sowing dates and genotypes had highly significant effect on plant height, leaves/stem ratio, total fresh, dry and protein forage yields for the two experiments, except total protein forage yield in experiment I among studied genotypes which was non-significant. While, the interaction between sowing dates x genotypes insignificant for all studied traits in the two experiments. The highest mean values of plant height obtained from the plants sown in fourth (March D4) and fifth sowing dates (April D5) sowing date were in the two experiments. While, sowing at November (D2) and December (D3) gave the highest mean values of leaves/stems ratio.