An apparatus and method for performing a real-time network antivirus function, which can perform, at high speed, real-time antivirus scanning on a transmission file in a network to be protected and blocking of a malicious file. The apparatus includes a packet processing unit for parsing input packets and outputting a transmission data stream, a packet-based checksum calculation unit for calculating a checksum of the transmission data stream for each packet, and outputting a signature included in the transmission data stream when a last packet of the transmission data stream is input, a virus scanning unit for performing virus scanning based on the signature, a detection and blocking unit for blocking each input packet or transmitting it to a destination, based on result of the virus scanning unit, and a caching unit for updating a blacklist, based on result of the detection and blocking unit.