Abstract: We present the three-dimensional (3D) growth of polypyrrole (PPy) microstructures with high aspect ratios (HAR) by a localized electropolymerization. The radicals formed by an oxidation of Py monomer is localized on the targeting area due to a confinement of electric field, forming a PPy structure. We found that a reversal point at which the relative field strengths of Ec (center of the grown structure) and Ee (edge) are reversed is a critical factor in determining the growth characteristic of the 3D PPy structure. A porous structure with open and closed pores is produced below the reversal point by the hydrogen bubble trapping in a gap between the microelectrode and the grown structure. Above the reversal point, a structure with dense and uniform features is obtained by a steady supply of monomer in the gap without bubble trapping.