Arl4D is a developmentally-regulated member of the ADP-ribosylation factor/ARF-like protein (ARF/Arl) family of Ras-related GTPases. Although Arl4 protein is reported to be expressed in adipose tissue, the function of Arl4D is unknown. To investigate the potential role of Arl4D in adipogenesis, we examined Arl4D expression during adipocyte differentiation and the effects of Arl4D overexpression on adipogenesis. Arl4D protein increased early in adipogenesis, with the highest expression at 4 h after adipogenesis initiation, followed by a decrease thereafter. Overexpression of Arl4D in 3T3-L1 cells potently inhibited their ability to differentiate and accumulate lipid, and reduced the expression of adipogenic genes. Furthermore, treatment with valproic acid, an Arl4D inducer, suppressed adipogenesis. These results suggest that rapid reduction of Arl4D is required for adipogenesis to proceed.