This letter proposes a throughput estimation technique for wireless local area network (WLAN) traffic in multiple channels using a software based packet analyzer. The proposed technique can artificially realize the simultaneous estimation of WLAN throughput in multiple channels by switching to a target channel at a high speed while running the software based packet analyzer. The proposed technique is evaluated using two types of WLAN traffic, i.e., constant bit rate traffic and variable bit rate traffic, which can simulate actual Web browsing behavior. Experimental results are presented to evaluate the proposed technique and validate its effectiveness.