A porous gold microelectrode (μAuE) was fabricated by dynamic soft templating and used for the square-wave anodic stripping analysis of As(III). The porous μAuE was fabricated by the electrodeposition of AuCl4− dissolved in a bicontinuous microemulsion (BME), which has an intertwined three-dimensional network composed of aqueous and oil phases compartmentalized by a surfactant and a cosurfuctant, and acts as a dynamic soft template. A 41.5-fold increase in electrochemically active surface area (ECSA) was confirmed after electrodeposition, while the microelectrode characteristics were still observed. Cyclic voltammetry revealed that the porous μAuE has abundant Au{100} and/or kink/step sites compared with bare μAuE. The overpotential for As(III) reduction decreased by 0.1 V at the porous μAuE, which may be due to exposed Au facets. A limit of detection (LOD) of less than 5 ppb and a wider linear range from 5 to 1000 ppb were confirmed when using the porous μAuE, which were due to the increased ECSA. In addition, the sensitivity at the porous μAuE was calculated to be 44.0 μA cm−2geo ppb−1, 14.4 times higher than that at the bare μAuE.