Copper matrix composites exhibit excellent mechanical and thermal properties. The composite consists of copper (Cu), zirconium (Zr), and boron (B) and is produced using the powder metallurgy technique. The high-energy ball milling was applied for mechanical alloying of the Cu-Zr-B powder mixture to achieve the desired ratio for obtaining a copper matrix reinforced with ZrB2 ceramic particles. The milling times of 10 and 40 hours for two different ball-to-powder ratios are investigated for a powder mixture with a composition of Cu-2.71Zr-2.27B (wt.%). XRD and SEM analyses were employed to determine structural and morphological changes in the mechanically alloyed powder mixture. Investigation of the morphological parameters shows that with prolonged milling, the shape of mixed particles becomes more uniform, while their structural parameters have been drastically changed. It is determined that during high-energy ball milling of the Cu-2.71Zr-2.27B (wt.%), the size of the copper powder decreases as the mechanical alloying increases for both ball-powder ratios. Dislocation densities reach their maximum value at around 30 hours of mechanical alloying for both ball-powder ratios, with dislocation density being higher for the 1:15 ratio, after which they decrease owing to the recrystallization of the copper matrix. XRD analysis shows no presence of ZrB2 reinforcement particles or oxides during milling.