Exchangeable Sodium Percentage (ESP) is a critical indicator of soil sodicity that strongly influences soil structure, chemical environment, and electromagnetic behavior, yet its role in controlling soil dielectric properties is rarely considered in microwave studies. This work investigates the effect of ESP on the complex dielectric permittivity of soils at C-band frequency (5.3 GHz) under controlled laboratory conditions. Soil samples spanning non-sodic to highly sodic classes were conditioned to a range of volumetric moisture contents, and the real (ε′) and imaginary (ε″) components of dielectric permittivity were measured using an open-ended coaxial probe technique. Results show that dielectric constant increases primarily with moisture content; however, at comparable moisture levels, soils with higher ESP consistently exhibit elevated ε′ values, particularly under wet conditions, due to sodium-induced structural changes and increased bound water contribution. More significantly, dielectric loss displays a strong and systematic dependence on ESP, increasing disproportionately with sodicity as a result of enhanced ionic conductivity and sodium mobility within the soil pore solution. The combined influence of moisture and ESP reveals threshold behavior, where sodicity-related conductive losses dominate dielectric response at moderate to high moisture levels. These findings demonstrate that sodicity-induced dielectric effects are independent of moisture alone and are not captured by conventional dielectric mixing models. The study highlights the need for ESP-aware dielectric parameterization to improve microwave modeling and soil characterization in salt-affected environments.