The compound of cage octa(cyclohexylsilsesquioxane)(c-C6H11)(8)Si8O12 was prepared in higher yield by the hydrolysis and polycondensation of trifunctional monomer (c-C6H11)Si(OC2H5)(3) in the mixtures of solvents of methyl isobutyl ketone and anhydrous ethanol with the concentration hydrochloric acid acting as the catalyst. The effects of reaction conditions, such as monomer concentration, the contents of water and catalyst were investigated. The results show that the better values of these reactive factors were 0.45 mol/L, H2O/XSiY3 = 3/1( molar ratio), Et4NOH/XSiY3 = 3 ( molar ratio), respectively. The existence of the higher boiling MIBK favours the higher reaction temperature, which accelerates the formation of octamer, reduces the reaction time and eventually increases the yield. The FTIR spectrum and H-1, C-13, and Si-29 NMR spectra show that the compound has the formula of (c-C6H11)(8)Si8O12 and the cage structure. The TG curve shows that the cage compound has a higher decomposition temperature, higher primary decomposition temperature and higher thermal residue and that the inorganic Si-O-Si composition does not change during the thermal processing. C (c) 2005 Springer Science + Business Media, Inc.