One aspect of a robot cleaner and a method for controlling the robot cleaner may include: a main body traveling along a floor surface to remove foreign matters in a cleaning driving mode; a sensor for sensing an obstacle around the main body; a side brush unit to extend a cleaning area by rotating; and a control unit to reduce the speed of the main body and to allow the main body to approach the obstacle ahead if the sensing sensor detects the area to where a plurality of the obstacles are contacted.
