A novel confined-space synthesis method has been developed to synthesize zeolite nanocrystals from colloidal silica nanoparticles. The silica nanoparticles function as a silica source as well as a hard template for zeolite nanocrystals. The synthetic zeolite nanocrystals possess similar size distribution corresponding to that of colloidal silica nanoparticles. As an example, zeolite NaA nanocrystals were produced from colloidal silica particles with a size range of 70-250 nm. Firstly, mesoporous silica-carbon composite was prepared by carbonization of a nanocomposite of silica particle, polyfurfuryl alcohol (FA)) and triblock copolymer surfactant (P123). Secondly, colloidal silica particles enclosed in the mesoporous carbon matrix were transformed into zeolite NaA nanocrystals in alkaline Na₂O-Al₂O₃ aqueous solution under hydrothermal conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ sorption were used to characterize the mesoporous carbon-silica composite and NaA nanocrystals. The amount of FA, aging time and hydrothermal time showed significant effects on the morphology and crystal size of NaA. NaA nanocrystals in a size range of 80-240 nm were prepared from the carbon-silica composite with a weight composition of 1 SiO₂: 2 P123: 5 FA, which was treated in an alkaline solution with a final molar ratio of 5.85 Na₂O: 1.00 Al₂O₃: 182 H₂O (on a basis of 1 SiO₂) at 80°C for 7h. The zeolite nanocrystals produced in this study would be useful for fabricating zeolite-polymer nancomposite membranes. Furthermore, the as-synthesized carbon-zeolite nanocomposite would be served as a new type hierarchical nanostructured adsorbent for wastewater treatment.