Hypocotyl elongation is critical for plants emerging from the soil, and serves as a model for investigating cell elongation mechanism. It has been reported that auxin biosynthesis enzyme YUCCAs (YUCs) and the cytoskeleton are involved in the regulation of hypocotyl elongation in Arabidopsis. However, whether and how the cytoskeleton is involved in YUCs-regulated hypocotyl elongation is not well understood. Here, we report that YUC3 directly interacted with Actin Depolymerizing Factor 4 (ADF4) to regulate hypocotyl elongation. The yuc3 mutant seedlings produced shorter hypocotyls, while YUC3-OEs seedlings showed longer hypocotyls. Pharmacological analysis showed that microfilament but not microtubule was involved in YUC3-regulated hypocotyl elongation. Consistent with this, defects in actin arrays were observed in the yuc3 seedlings. In addition, YUC3 interacted with ADF4 but not ADF1 in vitro and in vivo. Knock out of ADF4 partially rescued the defects of yuc3 mutant hypocotyl elongation and actin arrays. In summary, our results demonstrate that YUC3 mediates the organization of actin filaments possibly by interacting with ADF4 and affecting its actin depolymerizing/severing activity in the regulation of hypocotyl elongation.