A gateway, system and method for multiple radio access technology service are provided. The gateway is between base stations and a core network, including a receiving module, determining module and processing module. The receiving module receives a packet from the base stations or the core network through a tunnel between the base stations and the core network. The determining module determines whether the packet has a virtual IP header. If the packet has a virtual IP header, the processing module deletes the virtual IP header and replaces it with a tunnel header to transmit the packet to the core network through the tunnel by the tunnel header. If the packet has no virtual IP header, the processing module forwards the packet to the core network through the tunnel. The disclosure enhances transmitting and processing performance of the packet when the packet is transmitted through only a single tunnel.