A　small　crystal　NaY　zeolite　with　a　high　SiO2/Al2O3　ratio　was　successfully　synthesized　with　seeding　and　without　organic　template,　and　the　effects　of　the　silicon　source,　aging　time　and　Na2O　seeding　content　on　the　crystal　size　of　NaY　zeolite　were　investigated.　The　synthesized　samples　were　characterized　by　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM),　Fourier-Transform　Infrared　(FT-IR)　spectroscopy　and　N2　adsorption-desorption.　The　results　showed　that　the　silicon　source　used　to　prepare　seeding　had　a　great　effect　on　the　crystal　size　of　NaY　zeolite,　NaY　zeolite　with　average　size　of　100　nm　and　SiO2/Al2O3　ratio　of　5.42　was　obtained　by　using　the　seeding　prepared　with　silica　sol.　Moreover,　the　crystal　size　of　NaY　zeolite　decreased　with　an　extension　of　the　aging　time　and　an　increase　of　the　Na2O　content　of　seeding.　The　catalytic　performance　of　small　crystal　Y　zeolite　was　evaluated　in　the　hydrocracking　of　vacuum　gas　oil　(VGO),　the　catalyst　with　smaller　crystal　Y　zeolite　presented　higher　VGO　conversion　and　middle　distillates　selectivity　than　those　with　larger　ones　due　to　its　higher　surface　area　and　more　amount　of　mesoporous.　©　The　Royal　Society　of　Chemistry.