Coverage areas of WLAN access points (APs) are usually overlapped so a WLAN station (STA) might be able to find several APs to attach in a WLAN hotspot. Experimental results indicate that a WLAN STA normally associates with an AP with the maximal signal strength and requests the bandwidth of the AP for establishing network connections. However, this kind of STA-centric association and bandwidth request policy may introduce unbalance loads of APs, and the bandwidths of APs in a WLAN hotspot cannot be fully utilized. This unbalance load problem is a critical issue for the commercial deployment of voice over IP (VoIP) over WLAN (VoWLAN) service which has to maximize the number of concurrent VoWLAN sessions with Quality of Service (QoS) guarantees. In this paper, a novel dynamic load balancing scheme is proposed for a VoWLAN system. The network-assisted association policy first advices an STA to request a VoWLAN session through an AP with the minimal load. In case of the APs which the STA can attach are all overloaded, the proposed load balancing scheme further rearranges the serving VoWLAN STAs between APs in order to spare enough resources for accommodating that new request. Simulation results demonstrate that the reject rate of service requests for a VoWLAN system can be considerably reduced by employing the proposed scheme.