This study presents polymer-based neural microelectrodes whose electrically active sites are coated with platinum nanowires (Pt NWs). The Pt NWs are expected to enlarge the effective surface area of the active sites for better electrochemical performance, while keeping the geometrical surface area small enough for good spatial resolution. For the electrochemical and cytotoxicity study, two types of device were designed and fabricated using a 400 nm-thick platinum layer sandwiched between two 5 μm-thick polyimide insulation layers. A wet-chemical process at room temperature was introduced to synthesize Pt NWs on the active sites. Compared to conventional Pt electrodes, the fabricated electrodes showed a dramatic improvement of electrochemical properties: the cut-off frequency was reduced by 3 orders of magnitude and the cathodal charge storage capacity increased by a factor of 1,000. In a cytotoxicity study with a human neural cell line, the Pt NW-coated electrode did not show any significant effects on cell viability and metabolism compared to the control group.