This thesis proposes a refïned approach to evaluate iron losses of surface-mounted permanent magnet (PM) synchronous motors. PM synchronous moton have higher efficiency than induction machines with the same frame and same power ratnigs. However, in PM synchronous motors, iron losses form a larger portion of the total losses than in induction machines. Therefore, accurate calculation and minimization of iron losses is of particular importance in the design of PM synchronous motors. Although time-stepped FEM can provide good estimations of iron losses, it requires high effort and is very time-consuming for most designs and particularly for optimizations. Besides, FEM analysis can oniy be performed after the machine geometrical dimensions have been determined. In contrast, approximate analytical loss mode1 yields quick insight while requiring much less computation time and are readily available during the preliminary stage when the motor design is being iterated. Therefore, it is desirable to develop iron loss models that produce an acceptable prediction of the overall iron losses. In this thesis, simplified models for the estimation of tooth and yoke eddy current losses are developed based on the observations of FEM results and analytical analyses of the magnetic fields taking into account detailed geometrical effects. The effectiveness and limitations of the models are investigated. Correction factors are derived for geometrical influences. The nature of the flux density waveform has great impact on iron losses. Therefore, reduction of iron losses can be achieved by properly shaping the magnets, designing the slots and choosing appropriate number of poles. In order to test the proposed simplified loss models, measurements were performed on two surface-mounted PM synchronous motors. Particular attention was focused on the measmement of PWM wavefoms and decomposition of no-load losses. Experimental results of the two motors confirmed the validity of the proposed iron loss models.