Epitaxial morphotropic PbZr0.52Ti0.48O3 (PZT) thin films were employed to enhance the dielectric tunability of microwave filter devices without compromising the device impedance matching and low bias voltage (<10 V) requirements. Epitaxial heterostructure of ferroelectric PZT(001)/SrRuO3 (SRO) were grown on single crystal SrTiO3 (001) substrates by pulsed laser deposition, and a platinum (Pt) electrode was deposited on top of the PZT film. The tunability of the Pt/PZT/SRO varactor devices are strongly dependent on bias voltage and exhibited good dielectric tunability of 55% at 100 kHz and 10 V. The capacitance (CP) of the heteroepitaxial varactor devices was 105 pF at 10 V applied bias with a corresponding small leakage current of 1 nA. The influence of gamma (γ-ray) irradiation on the intrinsic electrical properties of the epitaxial PZT varactor devices was investigated as a function of the irradiation dose from 0 kGy to 400 kGy, in terms of the capacitance–voltage (C–V) characteristics and loss tangent response. With enhancing γ-ray irradiation doses the ferroelectric capacitance was found to decrease accompanying degradation in the loss tangent values. The results indicate that tunability of the epitaxial PZT ferroelectric thin-film capacitors decreased with increasing gamma irradiation dose and degraded ∼25% at 400 kGy dose than unexposed devices. Possible reasons for the degradation behavior of dielectric properties and tunability due to radiation-induced defects has been discussed. © 2016, The Minerals, Metals & Materials Society.