A capacitive sensor includes a sensing electrode, control unit, first and second comparator wherein the sensing electrode includes a first and a second conductors. A positive input terminal of the first comparator and a negative input terminal of the second comparator are coupled to the first conductor. A positive input terminal of the second comparator and a negative input terminal of the first comparator are coupled to the second conductor. The first and second comparators respectively output first and second comparing signals according to voltages of the positive and the negative terminals thereof. The control unit charges the first conductor and discharges the second conductor when the first and second comparing signals correspondingly are in first and second logic states. The control unit is operable on the contrary when the first and second comparing signals are in opposition to the abovementioned description.