A method for producing crystalline nanosized metal oxides by a supercritical seed enhanced crystallization ( SSEC) process has been developed. The process is a modified sol-gel process taking place at temperatures as low as 100 degrees C with supercritical CO2 as the solvent and polypropylene as the seeding material. The nanocrystalline product is obtained without having to resort to costly postreaction processing, and the product is obtained directly after the SSEC process. TiO2 powders produced by the SSEC process were shown to have a crystallinity of 60% and a crystal size of 7.3 +/- 2.5 nm. The crystallinity can be controlled by changing the heating rate of the initial formation of the nanoparticles, and the morphology can be altered by changing the process time.