We developed a flexible polyaniline film with a one-dimensional nanopillar array to achieve high electrochemical performance of a pH sensor. Soft lithography was used to prepare a highly ordered nanopillar array substrate. Gold was deposited on the nanopillar surface using a sputtering process to provide high electrical conductivity. Electropolymerization of aniline monomers was next performed on the gold nanopillar arrays. The electrodeposition of polyaniline was systematically investigated by controlling the scan rate and cycle number using a cyclic voltammetry technique. Highly ordered nanopillar arrays of polyaniline films were obtained under optimized conditions. The as-obtained electrode exhibited excellent electrochemical sensing performance, including sensitivity, repeatability, selectivity, and long-term stability. In addition, the sensing performance of the electrode was maintained even under a mechanically bent state.