Provided is an apparatus and method for transmitting packet data in a WSN. The apparatus for transmitting packet data in a WSN includes: a serial-to-parallel converter to parallel-convert information and output the converted information to two channel paths; a Walsh code pair generation unit to select an arbitrary Walsh code pair, mix the selected Walsh code pair with a pseudo noise (PN) code, and output one Walsh code to one channel path and the other Walsh code to the other channel path; a first mixer to mix the signals inputted to two channel paths, and generate a spread symbol for each path; a delay to delay the other channel path signal by a predetermined time; and a transmission unit to convert one channel path signal and the other channel path signal delayed by the delay into transmission frequency band signals, and transmit the converted signals as wireless signals.