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Melon (<i>Cucumis melo</i>) is an important economic crop cultivated worldwide. A unique <i>SUN</i> gene family plays a crucial role in regulating plant growth and fruit development, but many <i>SUN</i> family genes and their function have not been well-characterized in melon. In the present study, we performed genome-wide identification and bioinformatics analysis and identified 24 <i>CmSUN</i> family genes that contain integrated and conserved IQ67 domain in the melon genome. Transcriptome data analysis and qRT-PCR results showed that most <i>CmSUN</i>s are specifically enriched in melon reproductive organs, such as young flowers and ovaries. Through genetic transformation in melons, we found that overexpression of <i>CmSUN23-24</i> and <i>CmSUN25-26-27c</i> led to an increased fruit shape index, suggesting that they act as essential regulators in melon fruit shape variation. Subcellular localization revealed that the CmSUN23-24 protein is located in the cytoplasmic membrane. A direct interaction between CmSUN23-24 and a Calmodulin protein CmCaM5 was found by yeast two-hybrid assay, which indicated their participation in the calcium signal transduction pathway in regulating plant growth. These findings revealed the molecular characteristics, expression profile, and functional pattern of the <i>CmSUN</i> genes, and may provide the theoretical basis for the genetic improvement of melon fruit breeding.