In the mixed-line-rate (MLR) wavelength-division multiplexing (WDM) networks, each wavelength of fiber can provide different bandwidths (in 10/40/100 Gbps) by using different modulation types. Since the MLR-WDM technique is becoming the key and a cost-efficiency technique for the network upgrading, the problem for supporting virtual topology reconfiguration (VTR) becomes a very important issue. In this paper, the VTR problem for a MLR-WDM network is studied under dynamic traffic demand. By monitoring traffic of the lightpaths, a heuristic adaptation method is proposed to follow the changes in traffic without a priori knowledge of the future traffic pattern. The proposed can achieve the load balances by either adjusting (increasingly or decreasingly), adding or deleting one or more lightpaths at a time. Simulation experiments employing the adaptation algorithm on realistic network scenarios reveal interesting effects of the various system parameters. Specifically, we find that this method adapts very well to the changes in the offered traffic on MLR-WDM networks.