Fatty acid desaturases (FADS) are of great importance and play critical roles in regulating plant fatty acid (FA) compositions. But to date, no reports about characterization of the FAD genes have been reported in the model dicotyledonous grass species Medicago truncatula. In this study, using database searches, 20 full-length FAD genes were identified in M. truncatula. These FAD genes were unevenly distributed on six chromosomes except the chromosome 6 and 8. Phylogenetic analysis showed the FAD genes in M. truncatula were clustered into six subfamilies and had similar exon number and intron phase in the same subfamily. Moreover, expression analysis based on qRT-PCR indicated these FAD genes were extensively involved in cold and heat responses. This study would provide an important foundation for future cloning and functional studies of FAD genes in M. truncatula and other related legume species. (C) 2018 Elsevier Inc. All rights reserved.