Phospholipase D (PLD) and its product phosphatidic acid play important roles in cellular processes in plants including growth and developmentand stress responses. PLD genes constitute an important gene family in higher plants. The PLD family has been identified in Arabidopsis, rice, cotten and grape. In this study, 16 PLD genes were identified in the Medicago truncatula L. on the basis of protein domains, evolutionary relationship, gene architecture and sequence identity. They were grouped into six clads; α (4 genes), β (2 genes), γ (2 genes), δ (3 genes), ε (2 genes), ζ (2 gene) and φ (1 gene). The gene expression pattern of MtPLD4, MtPLD9 in the α subgroup and MtPLD13, MtPLD15 in the β/γ subgroup were investigated in four-week-old seedlings of Medicago truncatula under salt stress (23 ds/m NaCl) using qRT-PCR. MtPLD4 gene expression compared to that in control plants was increased 48 hr post-treatment. MtPLD13 gene expression decreased 48 hr post-treatment. Expression of the MtPLD9 and MtPLD15 genes increased in the early hours and then decreased compared to control plants. The results showed that the  α subgroup MtPLD genes in particular are valuable candidates for further functional genomics analysis.