A method of measuring a reference signal for positioning in a wireless communication system, includes receiving assistant data related to a plurality of cells including a reference cell and one or more neighbor cells for positioning; upon receiving the assistant data, calculating a reference signal time difference (RSTD) measurement value using: a first type reference signal of the plurality of cells, and a second type reference signal of the plurality of cells, wherein the first type reference signal is used for positioning, and wherein the second type reference signal is a reference signal commonly used within one cell; and reporting the RSTD measurement value to a location server.