This paper presents a study of the effect of contamination by solid particles on the dielectric characteristics of hydraulic oil. Studies have shown that contamination of the oil medium with bronze and graphite powder increases the complex dielectric constant, reaching a maximum at medium frequencies (100–400 kHz) and showing a different increase depending on the type of impurities. An increase in the dielectric constant by 24.4% for bronze powder and 13.4% for graphite powder at a concentration of 1.4% confirms the sensitivity of this parameter to the number and type of particles. In addition, measurements of the tangent of the loss angle demonstrated that graphite powder causes more significant losses at high frequencies, indicating its greater polarizability. The developed regression models with coefficients of determination and RMSE made it possible to approximate the dependences of dielectric parameters and the tangent of the loss angle on frequency and impurity content. The models have proven their high adequacy and low RMSE values, which makes them suitable for predicting pollution levels. These results open up prospects for using dielectric parameters to assess the condition of hydraulic systems and prevent their failures. The ease of integration of the measuring cells and their potential for portable solutions highlights the cost-effectiveness and versatility of the method, which will allow for rapid assessment of oil quality in the field.