New ferroelectric Ba0.85Sr0.15TiO3 (BST) thin films are deposited with different thicknesses (50,100, 200,280 and 400 nm) on silicon platinized substrates using spin coater machine and their morphological and structural properties are investigated. The results show that the films are well crystallized and that the perovskite phase is identified. The influence of BST film thickness on the dielectric characteristics of Au/Ba0.85Sr0.15TiO3/Pt capacitors are investigated and shows that the dielectric permittivity of the capacitors decreases with decreasing BST film thickness indicating the existence of a dead layer in the interfaces. Based on a series capacitor model, the dielectric permittivity and leakage current measurements, the thicknesses and dielectric permittivity of the dead layers on the Au/BST and BST/Pt interfaces are well investigated.