${\rm Ba}_{0.5}{\rmSr}_{0.5}{\rm TiO}_3$ (BST) thin films were depositedon sapphire substrate by RF magnetron sputtering techniques and interdigitalcapacitor (IDC) structures were fabricated using photolithography.Gamma irradiation induced changes of the BST based tunable capacitorhave been investigated under various doses from 0kGy to 600kGy.Structural and surface morphological studies have been carried outfor un-irradiated and irradiated film and revealed that the grainsizes and crystallinity are strongly depended on gamma irradiationdoses. The leakage current is increased with increasing gamma irradiationdoses due to creation of charge carriers and large numbers of defectin close proximity, provided path for charge carriers. The capacitanceof the IDC devices decreased with increasing gamma dose up to 50kGyand thereafter capacitance gradually increased with radiation dosesand reached higher than the un-irradiated device at 600kGy for1MHz frequency. The observed tunability ($∼ 25\% $)of the un-irradiated device was found nearly constant with gamma irradiationdoses. This study shows that gamma ray induced defects play importantrole to the electrical properties of the devices and the BST baseddevices are highly resistant to gamma radiation, which reflects possibleuse in space and nuclear applications.