An apparatus for removing a poison of a lambda sensor includes: a lambda sensor detecting an oxygen concentration included in an exhaust gas; and a control unit differentiating a heating temperature and a heating time to remove poison from the lambda sensor depending on a lambda signal output from the lambda sensor when a heating condition of the lambda sensor and an overrun section of an engine are satisfied. By heating the lambda sensor depending on the magnitude of the lambda signal output from the lambda sensor, the lambda sensor may be inhibited from being degraded by combusting the material poisoned to the electrode of the lambda sensor and the failure of the lambda sensor may be correctly determined.