LBD genes encode plant-specific transcription factors which play key roles in the regulation of lateral meristem development as well as response to environmental stress.The phylogenetic studies of LBD family in Medicago truncatula have not been reported yet.In this study,with the application of bioinformatics methods,we identified the LBD family genes of M.truncatula through the whole genome screening.The gene structure,phylogeny,evolutionary pressure,conserved domains,chromosomal localization and expression patterns were further analyzed.A total of 56 M.truncatula LBD genes,distributed unevenly on 8 chromosomes,were identified and were classified into 2 classes and 5 subfamilies.The exon numbers of all the genes were no more than two,indicating a simple gene structure of this family.The gene pairs had evolved under the influence of negative selection.The expression profiles of M.truncatula LBD genes showed a characteristic of temporal and tissue specificity,and regulated by drought and nitrogen stress.This study provides a theoretical foundation for verifying the function of LBD genes in M.truncatula.