Litz wire has been widely used in high-frequency electrical machines and transformers to minimize induced current loss and maintain high efficiency. Its heat dissipation capability can be a key design factor for high-power-density electrical machine and power electronics. Although litz wire equivalent thermal conductivity has been studied, its transposition effect is usually ignored. This paper focus on developing an analytical model to predict litz wire equivalent thermal conductivity considering its bundle transposition effects. A 3-D litz wire is modeled and simulated to validate analytical results. Also, transposed and parallel arrangement effects on litz wire equivalent thermal conductivity are compared and discussed. Hardware experiments are used to validate the analytical results in the end. The predictions of using the proposed analytical model match up well with both simulation and experimental results.