Expansins are proteins that have been reported to contribute to fruit softening. In this study, an expansin gene, CDK-Exp3, was identified from persimmon fruit, and the mRNA accumulation of CDK-Exp3 during postharvest softening was examined using real-time polymerase chain reaction (PCR). Sequence analysis showed that CDK-Exp3 contained a putative open reading frame of 765 bp encoding a polypeptide of 254 amino acid residues, which had all the characteristics of α-expansin. As fruit softened, the expression of CDK-Exp3 increased dramatically within the initial 8-day ripening at 20 °C followed by a gradual decline at the late stages of ripening. The expression of CDK-Exp3 was inhibited by gibberellic acid, and the maximum transcript abundance was delayed by 20 days compared with that of the control fruit. The results suggest that CDK-Exp3 might be closely related to softening of persimmon fruit during postharvest ripening.