This paper presents on the microwave properties of a loaded-line ferroelectric phase shifter based on (Ba, Sr)TiO 3 (BST) thin films for Ka-band applications. In order to reduce the dielectric loss of the BST thin film and its enhance a dielectric tunability, we optimized the deposition of Mn-doped (Ba 0.5 , Sr 0.5 )TiO 3 (Mn-BST) thin films on MgO substrates by using pulsed laser deposition (PLD). The crystallinity, microstructure and thickness of the thin films were investigated by using an X-ray diffractometer and a scanning electron microscope, respectively. We designed and fabricated a tunable ferroelectric capacitor loaded coplanar waveguide (CPW) type phase shifter to enhance the tuning and the loss characteristics of a conventional CPW ferroelectric phase shifter. The fabricated loaded-line phase shifter showed a low return loss of −15 dB in the frequency band from 25 GHz to 35 GHz. The differential phase shift was 293°, and the insertion loss decreased from −11.3 dB to −1.4 dB with increasing dc bias voltage from 0 to 80 V at 35 GHz.