Highly (100)-oriented BaTiO3 thin films having different thicknesses of 70-280nm were deposited on Pt/TiOx/SiO2/Si substrates with LaNiO3 as a buffer layer by one-step chemical Solution deposition. X-ray diffraction analyses showed that the LaNiO3 and BaTiO3 layers were all under tensile stress. The tensile stress of the LaNiO3 layer increased after depositing BaTiO3 films. The tensile stress in both the LaNiO3 and BaTiO3 layers decreased with increasing BaTiO3 layer thickness. The thickness dependences of the dielectric and piezoelectric behaviors of the highly (100)-oriented BaTiO3 films were investigated. It was found that the effect of tensile stress on the dielectric and piezoelectric properties is dominant. A reduction in in-plane tensile stress (primarily arising from a thermal expansion mismatch) was considered effective for increasing the dielectric and piezoelectric constants. The measured dielectric constant increased from about 313 for 70 nm films up to 831 for 280 nm films. The local effective piezoelectric coefficient increased from 15 pm/V for 70 nm films up to 45 pm/V for 280 nm films.