A method for transmitting a reference signal to a user equipment at a base station in a wireless communication system is disclosed. The method includes transmitting the reference signal to the user equipment according to a first pattern corresponding to a first rank and, if a rank is changed from the first rank to a second rank, transmitting the reference signal to the user equipment according to a second pattern corresponding to the second rank, wherein, if the second rank is greater than the first rank, the second pattern includes the first pattern. Preferably, the first pattern is a reference signal pattern for a single rank and the second pattern is defined as a hierarchical structure in which one or more reference signal symbols are added to the first pattern in a time domain direction.