An STBC based signal transmission method considering the number of symbols within a slot. In transmitting a signal using two or more transmission antennas in a mobile communication system using a structure in which one subframe includes two slots and each slot includes a plurality of symbols, transmission symbols are paired in units of two consecutive symbols within each subframe by an STBC scheme. The transmission symbols are mapped to a frequency region in units of slots and the mapped transmission symbols are transmitted. One symbol within a slot in which the number of symbols excluding symbols for transmitting a reference signal is an odd number is not paired by the STBC scheme.