The effect of using a tuning inductance on the performance of a Gilbert cell-based two level transistor CMOS sub-harmonic mixer is investigated. The tuning inductor used between the RF and LO switching stages causes conversion gain enhancement and noise figure improvement. Additionally, it compensates LO distortion due to the phase mismatch of LO signals in the sub-harmonic mixer. The design procedure is done in 0.18 :m CMOS process at 1.8 V supply voltage and 2.4 GHz frequency and reveals that the mixer has exhibited high performance after a FOM-based comparison, without increase the power consumption of 5 mW. The inductive connection between the RF and LO stages causes 7 dB enhancement of conversion gain and 7.3 and 6 dB improvement of noise figure and LO distortion, respectively while the mixer has achieved up to 8 dB conversion gain, 0.5 dBm IIP3, and 13.8 dB noise figure.