This paper presents analysis of the performance on the IEEE 802.11b in the presence of multiple IEEE 802.15.4 interferences. To analyze the performance, packet error rate (PER) and throughput are used as performance metrics. The PER is computed by the bit error rate (BER), the collision time and the number of IEEE 802.15.4 interferers in the presence of in-band of the IEEE 802.11b. The throughput of the IEEE 802.11b under multiple IEEE 802.15.4 interferences is obtained from the total IEEE 802.11b packet length received during a specified time. Analytic results of the performance of IEEE 802.11b under multiple IEEE 802.15.4 interferences are verified by simulation results. These results can support coexistence criteria for the IEEE 802.11b and the IEEE 802.15.4.