A method of receiving phase tracking reference signal (PT-RS) by a user equipment (UE) in a wireless communication system, the method includes determining one or more resource blocks to which the PT-RS is mapped among N resource blocks allocated to the UE; and receiving the PT-RS via the one or more second resource blocks, wherein the N resource blocks are indexed as second resource block indices 0 to N−1 from a resource block having a lowest index of first resource block indices to a resource block having a highest index of the first resource block indices, wherein the PT-RS is mapped to the one or more resource blocks having indices of the second resource block indices and the indices are determined based on a first value related to a frequency density of the PT-RS and a second value related to a resource block offset, wherein the first value is determined based on a scheduled bandwidth related with the N resource blocks allocated to the UE, and wherein N is a natural number.