In this paper, we have investigated the effects of microwave ovensover the IEEE 802.11 FHSS (Frequency Hopping Spread Spectrum) wirelessLAN card. The measured MAC Frame Error Rate (FER) and UDP Packet ErrorRate (PER) are affected by the microwave ovens. From these measurementresults we know that the performance of some channels within the IEEE802.11 FHSS wireless LAN card can be seriously deteriorated.Furthermore, decreasing the packet length would improve thetransmission performance from the PER measurement results. Therefore,we design a novel fuzzy controller to dynamically adjust the packetlength to against the interference from microwave oven. Simulationresults show that the designed fuzzy controller can effectivelyimprove the transmission performance in terms of throughput.