The most popular method of preparation of BaTiO3, which is one of the most widely used ferroelectric materials for multi-layered ceramic capacitors, is the solidstate reaction process between powdered barium carbonate (BaCO3) and titanium dioxide (TiO2) at high temperature. The influence of the different structural forms of TiO2 used (i.e. rutile or anatase) on the reaction process and on the crystallinity of synthesized BaTiO3 is only known on empirical grounds. The solid-state reaction between BaCO3 and either TiO2 anatase or TiO2 rutile was investigated by in situ by X-ray diffraction and micro Raman scattering measurements. The formation of both barium oxycarbonate BaOx(CO3)(1-x) and of a very small amount of Ba2TiO4 were detected in the samples as intermediate phase before the formation of BaTiO3. The Raman spectra of the final product obtained in each case is essentially the tetragonal BaTiO3 containing small amounts of non-reacting BaCO3 and of hexagonal barium titanate. The tetragonality of the final product was found to be slightly better for BaTiO3 synthesized from rutile and BaCO3 than from anatase and BaCO3, whereas the average particle sizes are essentially the same for both products.