The design and implementation of a Network Processor using System-on-a-chip(SoC) technology is presented. The proposed network processor can handle several protocols as well as various types of traffics simultaneously. The proposed SoC consists of ARM processor core, ATM block, AAL processing block, Ethernet block and a scheduler. The scheduler guarantees QoS of the voice traffic and supports multiple AAL2 packet. The SoC is manufactured on the 0.35 micron fabrication line of HYNIX semiconductor, the total number of gates is about 312,000, for a maximum operating frequency of over to 50㎒.