A multi-band mixer that can receive multiple band signals simultaneously is proposed. Using multiple local oscillator (LO) signals simultaneously, the mixer achieves independent gain control through relative power control of the multiple LO signals. Linear gain control is also achieved through multiple LO signal input with total LO power control. Theoretical analysis shows that a third-order nonlinearity component of the multiple LO signals supports linear conversion gain control. The measured test performances of a dual band receiving at the 300 MHz and 2.4 GHz bands supports the results of the theoretical analysis. Tests were conducted using a commercial double-balanced diode mixer and an MOSFET mixer we fabricated. Measurements confirm that linear control and independent control of conversion gain are achieved.