Aluminum trihydrate-filled poly(methyl methacrylate) (PMMA/ATH) is composite waste powder generated during the production of PMMA/ATH solid-surface composite sheets. It is estimated that 85,500 tons of this waste is being produced every year on a global scale. Since the information about it is scarce, this paper examines the physical characteristics of PMMA/ATH powder and the influence of milling upon its surface characteristics in order to determine its recycling and adhesion potentials. Non-milled powder particles show more irregular shape with more porous structure in comparison to milled powder. Milling causes the breaking of ATH particles in the PMMA matrix which leads to average particle size reduction and increased surface free energy. IGC results show higher values for than results derived by contact angle measurement. Nevertheless, the difference in values between non-milled and milled samples is even more obvious in IGC measurements than in contact angle measurements. The DSC curve of PMMA/ATH powder shows a typical thermal decomposition of aluminum hydroxides up to about 320 degrees C when an exothermic reaction is observed up to 445 degrees C, which is attributed to the burning of PMMA.