An apparatus and method for positioning a pilot in a transmitter for an Orthogonal Frequency Division Multiple Access (OFDMA) mobile communication system. In the apparatus, a consecutive block assignment determiner determines whether it will assign a consecutive block or a single block in a frequency axis or a time axis. A pilot tone pattern generator determines a pilot pattern in the block by applying a predetermined rule according to the determination result. A pilot tone inserter positions pilots in the block based on the determined pilot pattern.