Within the scope of the research, the characteristics of aluminium trihydrate-filled poly(methyl methacrylate) (PMMA/ATH) have been studied, and its compatibility with wood has been determined. The surface of PMMA/ATH has been modified with air plasma with dielectric barrier discharge. Changes of the chemical structure have been determined with x-ray photoelectron spectroscopy (XPS) and attenuated total reflection – infrared spectroscopy (ATR-FTIR). Confocal laser microscopy and atom force microscopy have been deployed to study the structure and morphology of the modified surfaces. The plasma treatments resulted in an etching of the matrix polymer, repolymerization and re-deposition of the etched PMMA material on the surface of the composite, which obliterated the positive impact of the plasma treatment. Surface free energy (SFE) measurements and adhesive bond strength tests were used to correlate the results of plasma effect to bonding PMMA/ATH with wood. Furthermore, the characteristics of PMMA/ATH powder have been analysed. Milling of the powder resulted in fracturing ATH particles in PMMA matrix and increase of SFE on account of its polar part. Differential scanning calorimetry (DSC) analysis of the powder showed a typical thermal decomposition of aluminium trihydrate up to about 320 °C, after which an exothermic reaction is observed up to 445 °C. It was concluded that PMMA/ATH powder is suitable for the production of a composite in a hot-press method. The surface of PMMA/ATH powder has been modified with ureido- and amino-functional silane coupling agents. XPS analysis of a modified powder confirmed chemically attached silanes on the surface of PMMA/ATH. With an increased surface modification rate, water contact angles decrease and the surface free energy of the modified powder increases. Modified PMMA/ATH powder was used in an alternative approach to producing wood-plastic composites (WPC) with the addition of wood particles and melamine-urea-formaldehyde resin (MUF). Mechanical tests of the composites indicate that the surface modification rate has a significant impact on the elastic modulus and modulus of rupture, while there are no significant differences between silanes used.