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The <i>GRAS</i> gene family is one of the most important families of transcriptional factors that have diverse functions in plant growth and developmental processes including axillary meristem patterning, signal-transduction, cell maintenance, phytohormone and light signaling. Despite their importance, the function of <i>GRAS</i> genes in pitaya fruit (<i>Selenicereus undatus</i> L.) remains unknown. Here, 45 members of the <i>HuGRAS</i> gene family were identified in the pitaya genome, which was distributed on 11 chromosomes. All 45 members of <i>HuGRAS</i> were grouped into nine subfamilies using phylogenetic analysis with six other species: maize, rice, soybeans, tomatoes, <i>Medicago truncatula</i> and Arabidopsis. Among the 45 genes, 12 genes were selected from RNA-Seq data due to their higher expression in different plant tissues of pitaya. In order to verify the RNA-Seq data, these 12 <i>HuGRAS</i> genes were subjected for qRT-PCR validation. Nine <i>HuGRAS</i> genes exhibited higher relative expression in different tissues of the plant. These nine genes which were categorized into six subfamilies inlcuding DELLA (<i>HuGRAS-1</i>), SCL-3 (<i>HuGRAS-7</i>), PAT1 (<i>HuGRAS-34</i>, <i>HuGRAS-35</i>, <i>HuGRAS-41</i>), HAM (<i>HuGRAS-37</i>), SCR (<i>HuGRAS-12</i>) and LISCL (<i>HuGRAS-18</i>, <i>HuGRAS-25</i>) might regulate growth and development in the pitaya plant. The results of the present study provide valuable information to improve tropical pitaya through a molecular and conventional breeding program.