A new method is proposed for the measurement of the dielectric properties of BaxSr1−xTiO3 (BST) thin films in the frequency range 106–1.8 × 109 Hz. A co-planar waveguide (CPW) transmission line was employed for impedance measurements via on-wafer probing. The measured impedance of the CPW line was found as a function of the probing position on the line. A simplified model of the CPW line under test allows the intrinsic dielectric properties of BST thin films to be extracted from the measured position-dependent impedance. Experimental results obtained by this new method agree well with those obtained by two-port S-parameters measurement at microwave frequencies using the same CPW structure.