<p>Characterizing hydrogeological parameters in fractured bedrock aquifers is essential for evaluating groundwater flow and solute transport. Conventional laboratory and field methods for parameter acquisition often prove impractical in fractured systems due to heterogeneous flow pathways, high costs, and installation constraints. This study aimed to estimate hydrogeological parameters of a fractured granite watershed in Shenzhen, China, using radium quartet and radon isotopes to overcome these limitations. Monthly sampling (June–December 2019) of two springs and a stream in the watershed enabled analysis of the main chemical constituents, radium quartet, and radon isotopes. The calculation of U/Th decay series retardation factors and recoil rates yielded: (1) the average groundwater residence time of the three sampling sites were 5.3, 9.7, and 2.6&#xa0;days; (2) the effective surface areas were 198.44 × 10⁴, 255.63 × 10⁴, and 1222.18 × 10⁴ cm²/L, with corresponding fracture widths of 10.75, 8.22, and 1.78&#xa0;μm; and (3) average hydraulic conductivities of 9.92 × 10⁵, 5.74 × 10⁵, and 0.28 × 10⁵&#xa0;m/s, respectively. Variations of estimated parameters were mainly influenced by the fluctuations of radium and radon activities in the groundwater. The factors influencing radium and radon activity included the hydraulic dynamics and interactions between groundwater and the host rock as well as the physical parameters and surficial chemical characteristics of the host rock. This study demonstrates the applicability of radionuclides for estimation of hydrogeological parameters in fractured bedrock regions. The reliability and limitations of the method are discussed to guide future applications.</p>