A method and an apparatus for maintaining information security in a video multicasting service are provided. The method includes: generating a network abstraction layer unit using received video information; encrypting the network abstraction layer unit of the video information; realtime transport protocol (RTP) packetizing the encrypted network abstraction layer unit of the video information; recording unit format information and field information, included in the network abstraction layer of the video information being stored in a memory, in a header extension field of the RTP header; and transmitting the RTP packet including the encrypted video information to a routing device.