Processing and material recovery of waste is an important aspect of environmental policy. Ash is waste in terms of legislation, but it is also a material that can be reused. Various works propose that biofuel ash could be used as inorganic fertilizer. The object of this work is based on using of wood ash (WA) from biomass and its modified form as the alternative filler in rubber mixtures. The WA samples with particle size of 25 and 40 µm were modified by silanization and properties of ash samples were characterized by elemental analysis (EDX), Scanning Electron Microscopy (SEM) and Fourier transformed infrared spectroscopy (FTIR). Model rubber blends were prepared by using modified wood ash as a partial replacement of conventional filler. Furthermore, the influence of the addition of ash on the cure characteristics (minimum torque – M_L, maximum torque – M_H, optimal cure time – t₉₀, scorch time t_s2), mechanical properties (tensile strength at break – TS_b, elongation at break –  E_b and hardness) and physical properties (cross-link density)  in sulfur-cured SBR composites were investigated. Dispersion of the WA filler and its incorporation into vulcanizates were based on observation of the fracture surfaces of vulcanizates by SEM. The results confirmed that the wood ash did not significantly affects the mechanical properties of the vulcanizates and can be used as a partial replacement of carbon black in SBR vulcanizates.