The nanorod-to-nanotube transition of a piezoelectric poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofiber inside cylindrical nanopores (CNP) with various pore diameters was precisely determined. After infiltrating the polymer into the CNP, a solid nanorod or hollow nanotube was obtained depending on the relative magnitude of the CNP diameter used compared to the critical pore diameter. The thickness of the lamellae formed inside the solid nanorod was found to be linearly dependent on the diameter of the nanocylinder. In addition, the wall thickness of the polymer nanotube increased with increasing nanocylinder diameter. The dependence of ferroelectric properties of the P(VDF-TrFE) nanofiber on the morphological transition were evaluated by measuring the piezoelectric polarization hysteresis loops. Compared to the hollow nanotube, the solid P(VDF-TrFE) nanorod showed significantly enhanced maximum polarization behavior, which is desirable for ferroelectric applications. These results show that the morphological transition from solid nanorod to hollow nanotube can play an important key role in the ferroelectric device fabrication of P(VDF-TrFE).