A simple and cost-effective method was proposed to synthesize nano-crystallized pure anatase titanium dioxide (TiO2) photocatalysts with a high thermal stability. The initial TiCl4 was reacted with a NaOH aqueous solution to form an amorphous sodium titanate, which was then transformed into an amorphous titanium dioxide hydrate through the replacement of Na+ by H+ using a HCl aqueous solution. After annealing, the pure nano-crystallized anatase TiO2 particles possessed a high thermal stability up to 900 A degrees C. The high concentration of NaOH aqueous solution played an important role in preventing the precipitation of rutile TiO2 during hydrolysis process and promoting the formation of the nano-crystallized anatase TiO2. Samples calcined at 800 A degrees C exhibited a significantly higher repeatable photocatalytic activity compared to the standard commercial photocatalyst P25 for the degradation of Rhodamine B in an aqueous suspension. This could be attributed to the synergistic effect of high crystallinity and mesoporous structure. The method is very simple, template-free, and cost effective, which makes it potential for the large-scale production.