Disclosed is a system and method for demodulating packet data channels with multiple Walsh codes in a CDMA mobile communication system supporting voice and packet data services. A plurality of fingers process signals received from a transmitter as inputs, perform despreading and channel compensation with spreading codes pre-assigned to the transmitter, and outputting the despread chip signals. A chip combiner combines the chip signals output from the plurality of fingers. A chip buffer stores the combined chip signals until decoding of the packet data control channels is completed and information on the multiple Walsh codes assigned to the packet data channels. Then, a multiple Walsh demodulator generates at least one Walsh symbol performing Walsh decovering of the combined chip signals using information on the multiple Walsh codes. Therefore, the system can efficiently demodulate data transmission channels using the multiple Walsh codes, and thus complexity of the system and demodulation time can be reduced.