The Red River fault zone (RRFZ), situated along the southeastern margin of the Tibetan Plateau, between the Yangtze-South China and the Indochina blocks, is a large-scale strike-slip fault zone that intersects the crust and undergoes intense shear deformation. Geophysical investigations revealed that high-conductivity anomalies are distributed within this fault zone in the middle to lower crust. Nevertheless, systematic laboratory measurements of electrical conductivity for fault rocks, particularly those from the RRFZ, remain critically underexplored. To address this gap, we performed experimental measurements on the electrical conductivity of cataclasite and mylonite collected from the ductile shear zone of the southern segment of the RRFZ. The investigated samples, collected from Yuanyang County (Yunnan Province, SW China), represent archetypal fault rocks of mid-crustal ductile shear zone. Our experimental results showed that: (a) Under ambient temperature conditions, the electrical conductivity of the cataclasites with ultrafine-grained size matrices exhibited a marked enhancement to ~ 10^-5 S/m as the pressure increased to 600 MPa. Conversely, the mylonites showed insulating behavior, i.e., the electrical conductivity decreased slightly in the order of 10^-9 S/m even when the pressure increased to 1.4 GPa. (b) When the temperature increased to > 600 ℃, the electrical conductivity of all fault rocks increased significantly to > 10^-5 S/m, and the logarithm of the conductivity is approximately linearly related to the inverse of the temperature, following the Arrhenius law. Since fault rocks with ultra-fine particles have a larger specific surface area, it is speculated that the grain boundary diffusion of the charge carriers in the fine-grained fault rocks constitutes a plausible mechanism for the observed high-conductivity anomalies in the RRFZ. These experimental results provide a reference for exploring the electrical structure of the RRFZ, and even other fault zones.