In neuronal development, dendritic outgrowth and arborization are important for the establishment of neural circuit formation. A previous study reported that PSD-95-interacting regulator of spine morphogenesis (Preso) formed a complex with PAK-interacting exchange factor-beta (βPix) via PSD-95/Dlg/ZO-1 (PDZ) interaction. Here, we report that Preso and its binding protein, βPix, are localized in dendritic growth cones. Knockdown and dominant-negative inhibition of Preso in cultured neurons markedly reduced the dendritic outgrowth but not branching, and led to a decrease in the intensity of βPix and F-actin in neuronal dendritic tips. Moreover, phosphatidylinositol 4,5-bisphosphate (PIP2) induced a conformational change in Preso toward the open PDZ domain and enhanced the interaction with βPix. In addition, the Preso band 4.1 protein, ezrin, radixin and moesin (FERM) domain mutant is unable to interact with PIP2 and it did not rescue the Preso-knockdown effect. These results indicate that PIP2 is a key signalling molecule that regulates dendritic outgrowth through activation of small GTPase signalling via interaction between Preso and βPix.