Disclosed is a robot cleaner including: a main body forming an outer shape; a pair of rotary mops moving the main body while rotating in contact with a floor; a drive motor rotating the pair of rotary mops; a pump connected to a water tank and driving a nozzle for spraying water to the rotary mop; and a controller for determining water content of the rotary mop in a preliminary step before wet cleaning, and controlling to start the wet cleaning after driving the pump until the water content of the rotary mop satisfy a certain level. Accordingly, it is possible to detect a change in the output current of the motor of the rotary mop of the robot cleaner and determine the water content according to the change in the current value.