Femtocells are small base stations that are usually installed in indoor environments to improve the data rate in coverage holes of cellular systems. Since femtocells are usually deployed in an ad hoc manner by users and share the same frequency bands, interference mitigation becomes the main concerns of resource management function. In this paper, we consider the OFDMA-based femtocell networks, and treat the resource allocation problem by developing dynamic subchannel assignment and power allocation algorithms. The proposed algorithms utilize the user diversity within femtocells and take into account the interference conditions of local and neighboring femtocells. The simulation results show that such dynamic resource assignment provide higher system throughput as well as per-user QoS. Additionally subchannel usage ratio is increased.