This paper presents the results of synthesis of nanozeolite NaX from Vietnamese kaolin. Influence factors on the control of crystal sizes and application of synthesized materials as adsorbent for organic compound are discussed. The results show that there are several factors that influence the synthesis. When water content in gel increases, crystal size of NaX increases sharply. The increase of alkaline and silica contents increases the crystallinity and decreases the particle size of nano NaX, and the particle size reaches the minimum at Na2O/Al2O3 = 5.0 and SiO2/Al2O3 = 4.0. Crystal sizes formed at low crystallizing temperature are smaller than those formed at higher temperature. Ageing time and crystallizing time strongly influence the crystallinity and crystal size, which is related to the number of crystal seeds formed during ageing period, the growth of seed and the partial solubility of crystal at maximum formation. Nano NaX was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) adsorption, Fourier transform infrared (FTIR) and simultaneous thermogravimetry-differential scanning calorimetry (TG/DSC). At optimized synthesis conditions, nano NaX has surface area of 573 m2/g with external surface area of 92 m2/g, pore size distribution at 0.81 and 10.8 nm, average crystal size of 25 nm and thermal stability up to 789°C. This material can adsorb cumene rapidly with high adsorption capacity and stability.