MoO3 organosol was obtained by using surface active agent CTAB to modify the nanoparticles in MoO3 hydrosol and n-pentanol to extract MoO3 nanoparticles modified by CTAB. The effect factors on organosol were discussed systematically. TEM photos showed that the MoO3 nanoparticles were spherical in shape, the size was about 40 nm, particle size distribution was in narrow range. ED images indicated that the MoO3 nanoparticles were polycrystalline structure. UV-VIS analysis showed that the MoO3 nanoparticles organosol had good photochromic effect.