Bismuth ferrite (BiFeO3) thin films with Bi2O3 buffer layers were prepared on Si/SiO2/TiO2/Pt substrates by sol-gel-derived spin-coating method. The structural and electrical properties of BiFeO3 was effectively improved by adding a Bi2O3 buffer layers either at Pt/BiFeO3 interface or on BiFeO3 surface, also strongly depending on the positions and the annealing conditions of buffer layers. A 500 degrees C-annealed Bi2O3 buffer layer could act as a Bi source for compensating Bi volatilization and a diffusion barrier for species from BiFeO3. A near stoichiometric BiFeO3 with less defects and substrate contamination was obtained by employing a 500 degrees C-annealed Bi2O3 buffer layer in between Pt substrate and BiFeO3. The structure change in BiFeO3 led by such a buffer layer should result from the interfacial constraint between buffer layer and BiFeO3. Furthermore, this crystalline BiFeO3 specimen exhibited a highly (100)-textured, where this preferred orientation was attributed to the accumulation of Bi at Pt/BFO interface. Therefore, the Pt/500 degrees C-annealed Bi2O3/BiFeO3/Pt thin film exhibited the good ferroelectric and magnetic properties. As compared to the usual method for controlling BiFeO3 composition by adding excess Bi, this study indicates the more advantages using a Bi2O3 buffer layer.