Abstract: Using sodium silicate and sodium aluminate as raw materials, NaY zeolites were synthesized by direct crystallization without seed gel. The hydrothermal synthesis conditions including aging time, crystallization temperature and time, water content and n(Na2O)/n(SiO2) in the system were investigated in detail. The synthesized zeolites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that increasing aging time favors the formation of more nuclears, but too long aging time leads to increase particle size of zeolite. Prolonging crystal temperature and time increases the crystallinity of NaY zeolite, while transcrystalliziation phenomena occur easily and lead to mixedcrystal. The crystallinity of product is highly affected by n(Na2O)/n(SiO2) and n(H2O)/n(Al2O3). High crystallinity NaY zeolites are synthesized when n（Na2O）/n(SiO2) and n(H2O)/n(Al2O3) are 1.0 and 160, respectively.