A novel scheme for polarization insensitive optical wavelength conversion based on four wave mixing (FWM) in semiconductor optical amplifier (SOA) is proposed and demonstrated. An all optical polarization state converter which can automatically change random input polarization state into linear output polarization state with fixed polarization direction and power is employed in wavelength converter. Using it to control the polarization state of signal beam, the intrinsical polarization sensitivity of FWM process can be overcome simply.