A new low-cost demodulator for ZigBee receivers satisfying requirements of IEEE802.15.4 standard is presented, which is designed for ISM 2.4 GHz band and based on Zero-IF receivers. This demodulator extracts symbols directly from baseband signal rather than recovering PN code chips, so its structure is simple. Two main techniques are used to improve the performance of demodulator. One is Phase-Axis Crossing Detector (PACD) which detects the phase correlation of baseband signal. The other is symbol synchronization and sampling clock correction algorithm. The result shows that this demodulator performance, Symbol Error Rate (SER) and Packet Error Rate (PER) meet IEEE 802.15.4TM standard requirements and the demodulator can handle frequency offset in excess of 200 kHz, involving a Zero-IF receiver with a Noise Figure (NF) lower than 17 dB, which is easily implemented in standard CMOS technology.