A method of transmitting/updating system informations is disclosed. The present invention includes transmitting channel descriptor transmission control information including an index of the system information classified into a plurality of groups to a terminal at a start timing point of an arbitrary control interval and transmitting the system information of a corresponding group to the terminal at a transmission timing point according to the index in the control interval. According to the above embodiments of the present invention, it is able to non-periodically perform scheduling on system informations classified by a base station. It is able to decrease an update time of system information as well as a time taken for network entry and initialization of terminals. And, it is able to obtain distributed effect of an initial ranging attempt in aspect of system.