We describe an optical fiber based setup for performing polarization resolved magneto-optical spectroscopy measurements under low temperatures ( approximately 4 K) and high magnetic fields ( approximately 8 T). The measurements are performed in a windowless helium Dewar. Circularly polarized light is produced inside the Dewar by inserting the polarizing elements between the fiber end and the sample. Photoconductivity spectra of a GaAs/AlGaAs multiquantum-well sample have been measured over the photon energy range of 1.5-1.7 eV in left and right circularly polarized light under crossed magnetic and electric fields. It is shown that reversing the direction of magnetic field produces the same spectral changes as caused by changing the direction of circular polarization with the optical components.