Improvement of electric property of degraded(Ba, Sr)$TiO_3$ thin film due to $TiO_2$layer has been investigated. SBT thin film was deposited on Pt/Ti/$SiO_2$/Si substrate by RF magnerton sputter suing insitu process. Undersirable layer with low dielectric constant, $TiO_2$, at BST/Pt interface was confirmed by AES depth profile, XRD. Electric properties of BST thin film were improved by removing $TiO_2$ layer. Excess BaO and SeO were added to BST target for supplement of deficient Ba, Sr content in BST thin film. As the (Ba+Sr)/Ti ratio variation, the $TiO_2$ layer was removed and the dielectrci property of BST thin film was improved. At (Ba+Sr)/Ti=1.05, dielectric constant showed its highst value of 510. The leakage current of BST was almost independent of the existence of $TiO_2$ layer.