Abstract: The process of nucleation and crystal growth of NaY zeolite is studied with the addition into the hydrothermal system Na₂O/Al₂O₃/SiO₂/H₂O of crystallization directing agent or NaX zeolite as seed crystal over the temperature range 55℃～100℃,and the apparent activation energy for nucleation and crystal growth is calculated.As NaX zeolite can grow at the surface of NaX crystal,the activation energy of nucleation decreases sharply in the presence of NaX zeolite as seed crystal.Alumino-silicate gel is used as crystallization directing agent in the experiments.Changes with aging time of the directing activity of the gel itself and the gel in liquid-phase and solid-phase are examined at 32℃,together with the mechanism of the formation of NaY zeolite in the presence of the crystallization directing agent.The results of experiments show that the directing activity of alumino-silicate gel in liquid-phase excels that of tbe gel itself.