Ba0.5Sr0.5TiO3 (BST) thin films were prepared on a very thin buffer layer of the same BST by r.f. sputtering. The conditions for the deposition of the buffer layer were changed by varying the deposition temperature, deposition rate and thickness, and then the effects were investigated. BST on a buffer layer deposited at 700 degrees C crystallized at the deposition temperature of 250 degrees C without any post-annealing. As the deposition rate of buffer layer decreased from 2.2 nm/min to 0.25 nm/min, the crystal orientation was changed from random to (111) preferred orientation. In the case of 20 nm thick BST film having a 10 nm thick buffer layer deposited at 700 degrees C, SiO2 effective thickness showed the value of about 0.26 nm and leakage current density of about 10(-8) A/cm(2) could be maintained up to 2.3 V.