Although the extreme miniaturization of components in integrated circuits and biochemical chips has driven the development of various nanofabrication technologies, the 3D fabrication of nanoscale objects is still in its infancy. Here we propose a novel method to fabricate a free-standing nanowall by the precise, repetitive deposition of electrospun polymer nanofibers. We show that the electrified nanojet, which tends to become unstable when traveling in air because of coulombic repulsion, can be stably focused onto the microline of a metal electrode. On the conducting line, the polymer nanojet is spontaneously stacked successively to form a wall-like structure. We rationalize the length of the wall by balancing the tension in the polymer fiber with the electrostatic interaction of the fiber with the metal ground. We also show that the length of a nanowall can be controlled by translating the substrate. This novel 3D printing scheme can be applied to the development of various 3D nanoscale objects including bioscaffolds, nanofilters, nanorobots, and nanoelectrodes.