Heterogeneous network (HetNet) is expected to be widely deployed in 4G cellular systems such as LTE-Advanced. One important requirement for LTE/LTE-Advanced networks is to support seamless and robust mobility so that a user can be handed over from one cell to another smoothly without service disruption. To ensure satisfactory user experience, 3GPP has started a study to evaluate the performance of mobility in HetNet and possibly make enhancement to improve mobility in HetNet. The main objective of this paper is to evaluate the mobility performance in HetNet based on the 3GPP study item simulation framework. The impact of HetNet on mobility is characterized for various user speeds and small cell densities. Our simulation result shows that compared to conventional macro-only layout, deployment of small cells poses challenges for mobility management. HetNet increases the probability of handover failure, especially if the user speed is high. Existing methods such as MSE based handover does not work well in HetNet either. Therefore more intelligent mobility management method is needed to enhance mobility management in HetNet.