The present invention provides a method for performing positioning by a terminal in a wireless communication system including: receiving assistance data including reference cell information (ReferenceCellInfo) and neighboring cell information (NeighbourCellInfo) from a serving base station; receiving a positioning reference signal from each of a reference cell and at least one neighboring cell based on the received assistance data; measuring a reference signal time difference (RSTD) for the reference cell of at least one neighboring cell by using the received positioning reference signal; and reporting the measured RSTD to the serving base station.