A method for measuring a Synchronization Signal Block (SSB) by a terminal in a wireless communication system. In particular, the method may include: receiving a cell list including information of at least one first cell, first SSB transmission periodicity information for the at least one cell, and second SSB transmission periodicity information for a second cell that is not included in the cell list; measuring Reference Signal Received Power (RSRP) for an SSB of the at least one first cell based on a first SSB measurement window, which is set up by using the first SSB transmission periodicity information; and measuring RSRP for an SSB of the second cell based on a second SSB measurement window, which is set up by using the second SSB transmission periodicity information.