YABBY genes are plant-specific transcription factors (TF) that function in plant growth and development.  To investigate the functions of the YABBY genes in plants’ stress tolerance, we analyzed the YABBY genes in foxtail millet (Setaria italica) and investigated their functions on plant growth and responses to different stresses.  Eight YABBY genes were identified on five chromosomes. These genes showed strong relationships with YABBY genes in other monocot species.  Phylogenetical SiYABs were classified into four clades: FIL/YAB3, YAB2, INO, and CRC.  No monocot YABBY member was classified into the YAB5 clade.  Four conserved motifs were identified and motif 1 constituted the YABBY domain, whereas motifs 2 and 3 formed the C2-C2 region. SiYAB genes were highly expressed in reproductive tissues.  Among all the SiYABs, SiDL was selected to be overexpressed in Arabidopsis thaliana to check the functions of the YABBY genes.  Overexpression of SiDL in Arabidopsis thaliana caused delayed flowering, leaf curling, and reduced seed size.  In addition, SiDL acted as a negative regulator in plant response to salt stress. Our study provides information to assist the study of YABBY gene function in S. italica.