The　effects　of　phosphorus　on　the　structure　and　hydrofining　performance　of　tri-metallic　WMoNi/Al2O3　catalysts　prepared　with　W/Mo-based　hybrid　precursor　nanocrystals　were　investigated.　The　incorporation　of　phosphorus　weakened　the　metal-support　interactions　(MSIs)　and　facilitated　the　formation　of　more　synergetic　NiWMoS　phases　with　higher　stacks.　Catalytic　tests　using　a　fluid　catalytic　cracking　diesel　fuel　showed　that　the　changes　in　the　MSIs　and　the　morphology　of　the　active　phases　had　a　more　positive　effect　on　the　hydrodenitrogenation　activity　than　on　the　hydrodesulfurization　activity.　In　contrast,　when　phosphorus　was　incorporated　into　a　tri-metallic　WMoNiP/Al2O3　catalyst　prepared　by　a　conventional　incipient　impregnation　method,　the　MSIs　decreased　causing　aggregation　of　the　metal　species　which　resulted　in　poorer　hydrofining　performance　of　the　catalyst.　These　results　show　that　incorporating　phosphorus　into　a　WMoNi/Al2O3　catalyst　can　finely　tune　the　structure　of　the　active　phase　to　enhance　the　hydrogenation　and　hydrodenitrogenation　activity　of　the　resulting　tri-metallic　catalyst.