The present invention relates to a broadband wireless access system including a femto cell, and more particularly, to a method of low duty operation in a femto base station. According to one embodiment of the present invention, in a broadband wireless access system, a method of a low duty mode operation of a femto base station saving power includes the steps of determining a low duty mode pattern to be performed by the femto base station according to a preset reference and performing the low duty mode operation according to the determined pattern. In this case, the preset reference can include at least one selected from the group consisting of a battery level, an available resource status and a subscriber type of the femto base station.