In this study, we investigated the effects of high-dose gamma-ray irradiation on the mechanical and dielectric properties of polypropylene (PP)-basalt thick films. PP-basalt thick-film composites with various basalt contents from 0.5 to 10.0% were prepared by a hot-press method. The samples were exposed to gamma radiation at different doses in the range 3-25 kGy. The mechanical properties of the samples, such as the Young's modulus, tensile strength, percentage strain at break, and energy at break, were examined in the context of the gamma-irradiation process. Although the maximum elasticity was obtained for the unirradiated 0.5% basalt-added composite, the 6 kGy gamma-irradiated PP-1.0% basalt sample exhibited the highest elasticity properties among all of the composites. The best mechanical properties, including the ultimate tensile strength and energy at break values, were achieved for the 12 kGy gamma-irradiated neat PP. The dielectric properties of the PP-basalt composites were also investigated in the 100 Hz to 15 MHz frequency region at room temperature. According to the analysis of the dielectric properties, the 3 kGy gamma-irradiated neat PP may have potential for microelectronic device applications that require low dielectric constant and dielectric loss materials. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47414.