A common mode noise reduction circuit includes at least one first input end, at least one second input end, at least one first output end, and at least one second output end. The circuit is further provided with at least one resistor, at least one inductor, and at least one capacitor, symmetrically disposed within the circuit loop defined by the four ends. Common mode noise, after entering the circuit, is transformed into heat by the resistance of the circuit such that the common mode noise is suppressed. Differential mode signals, on the contrary, after entering the circuit, can pass through the circuit with minimum loss.