A method of reporting, by user equipment, system information in a wireless communication system, the method comprising: Transmitting a ready-acquired system information availability indicator, notifying a serving cell that ready-acquired system information about a neighboring cell is present, to the serving cell; receiving a system information reporting request from the serving cell; and sending a system information report to the serving cell in response to the system reporting request, wherein: if the system information reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the ready-acquired system information is to be reported, the system information report comprises the ready-acquired system information, and if the system reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the system information is to be acquired from the neighboring cell and to be reported, the user equipment acquires new system information from the neighboring cell and reports the newly acquired system information to the serving cell; and wherein the ready-acquired system information is system information acquired from the neighboring cell before receiving the system reporting request. Transmitting a ready-acquired system information availability indicator, notifying a serving cell that ready-acquired system information about a neighboring cell is present, to the serving cell; receiving a system information reporting request from the serving cell; and sending a system information report to the serving cell in response to the system reporting request, wherein: if the system information reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the ready-acquired system information is to be reported, the system information report comprises the ready-acquired system information, and if the system reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the system information is to be acquired from the neighboring cell and to be reported, the user equipment acquires new system information from the neighboring cell and reports the newly acquired system information to the serving cell; and if the system information reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the ready-acquired system information is to be reported, the system information report comprises the ready-acquired system information, and if the system reporting request comprises a ready-acquired system information reporting request indicator and the ready-acquired system information reporting request indicator indicates that the system information is to be acquired from the neighboring cell and to be reported, the user equipment acquires new system information from the neighboring cell and reports the newly acquired system information to the serving cell; and wherein the ready-acquired system information is system information acquired from the neighboring cell before receiving the system reporting request.