The present invention provides a method of a node sending frames in a Cognitive Radio (CR) system. The method of the node includes being allocated a first channel as an operating channel where the node will be operated, sensing one or more candidate channels available as the operating channel of the node, determining whether to extend a frequency bandwidth of the operating channel, in addition to the first channel, based on a result of the sense for the one or more candidate channels, and sending the frames using a frequency bandwidth extended by adding a second channel, newly determined as the operating channel, to the first channel according to the determination.