An apparatus for updating a database for wireless LAN based positioning includes a database for storing grid cells divided by pCell ID and base station-derived environment information and wireless LAN environment information matched to the grid cells; a grid cell determining unit for determining an information-unmeasured grid cell among the grid cells, the information-unmeasured grid cell being a grid cell that has unmeasured information among parameters of the wireless LAN environment information matched to the grid cells; an unmeasured parameter checking unit for checking an unmeasured parameter in the information-unmeasured grid cell; a radiowave environment estimating unit for generating radiowave environment estimation information by estimating the unmeasured information based on the unmeasured parameter checked; and a database updating unit for reflecting the radiowave environment estimation information in the information-unmeasured grid cell determined.