A robot cleaner may include a main body; a traveling assembly moving the main body; a cleaning tool assembly installed in the lower part of the main body, and contacting a floor to clean the floor; a water-feeding unit supplying water to the cleaning tool assembly; and a capacitance measurer contacting the cleaning tool assembly, and measuring capacitance of the cleaning tool assembly in order to calculate an amount of water of the cleaning tool assembly. Accordingly, by measuring an amount of water of a cleaning tool installed in a robot cleaner based on capacitance, it is possible to accurately measure an amount of water absorbed in a cleaning tool.