Hydrodearomatization (HDA), hydrodenitrogenation (HDN) and hydrodesulphurization (HDS) of real gas oils (various sulphur, nitrogen and total aromatic content) was investigated over Pd, Pt catalysts supported on USY zeolite, whose Pd/Pt mass ratio was varied between 6:1 and 1:3, and total metal contents were between 0.90 and 0.93. The effect of Pd/Pt ratio on HDA, HDN and HDS activities is presented. The advantageous process parameters for HDA, HDN and HDS of gas oils over a selected catalyst (e.g. Pd/Pt mass ratio 3:1) were determined. Additionally, the effect of key process parameters (temperature, pressure, LHSV) on the yield and quality of products was studied. Under optimal process parameters the HDA efficiency decreased with sulphur and nitrogen content of feed. The rate of HDA enhanced with Pt content of the catalyst while HDS and HDN efficiency increased with Pd content. The maximum aromatic saturation was 85% and it decreased with sulphur and nitrogen content of the feed.