Carbosilane fine particles were synthesized by core-crosslinking of carbo-silane block copolymer micelles and they were pyrolytically transformed into silica nanoparticles. The carbosilane block copolymer, poly(1-(3-butenyl)-1-methylsilacyclo-butane)-block-polystyrene, (polyBMSB-b-polySt), [(m, n) = (31, 16), (54, 30), and (75, 28)], was synthesized by anionic polymerization of BMSB and St, where m and n represent polymerization degrees of BMSB and St segments, respectively. The block copolymer formed micelles in N,N-dimethylformamide (DMF). The hydrodynamic diameters (D-h) of the micelles evaluated by dynamic light scattering ranged from 40 to 158 nm depending on the copolymer molecular weight. The core of the micelle was cross-linked by Pt-catalyzed hydrosilation with 1,2-bis(dimethylsilylethane). The Dh of the core-cross-linked micelles in THF ranged from 56 to 164 nm. These precursor particles were pyrolyzed at 850 degrees C under N-2 to give ceramic nanoparticles. The diameters of the spherical ceramic particles estimated by AFM ranged from 25 to 60 nm. X-ray fluorescence analysis of the ceramic products revealed that it consisted of mainly SiO2 rather than SiC. (c) 2005 Wiley Periodicals, Inc.