A mapping method and an apparatus, which uniformly distribute bits included in transmission symbols to various resource blocks in mapping the transmission symbols to the resource blocks for transmission in an OFDMA mobile communication system. A sub-packet generator generates a sub-packet by selecting symbols from coded symbols including a first bit group and a second bit group, the first bit group having a different priority than the second bit group. A divider divides each bit group of the sub-packet into as many bit streams as previously allocated resource blocks. A resource block mapper maps the divided bit streams to the resource blocks, respectively, and outputs the bit streams for transmission.