Introduction. Friction stir processing (FSP) is recognized as a promising method for surface layer modification of structural copper‑based alloys; however, the high thermal conductivity of this class of materials significantly complicates thermal cycle management and, consequently, microstructural control. The present work is devoted to a systematic study of the effect of controlled heat removal – both air cooling and water cooling – during single‑pass FSP on the structural‑phase state and the resulting mechanical properties of a series of commercial copper alloys. The purpose of the study is to establish the relationship between the intensity of forced cooling, the thermophysical properties of the alloys, and the resulting grain morphology in the stir zone, which determines the level of service properties of the processed materials. Methods. The following alloys were selected as research objects: 89 Cu–9 Al–2 Mn, 93.35 Cu–6.5 Sn–0.15 P, 96 Cu–3 Si–1 Mn, and 63 Cu-37 Zn. FSP was performed in a single pass on a specialized experimental setup at ISPMS SB RAS using a tool fabricated of the nickel‑based superalloy ZhS6U. Active heat removal was realized by immersing the workpiece in flowing water, circulating coolant through the tool body, and directing a water jet into the contact zone; compressed air blowing was used as an alternative cooling scheme. Macro‑ and microstructure were investigated using optical metallography, scanning and transmission electron microscopy, X‑ray diffraction analysis, and energy‑dispersive spectroscopy. Mechanical properties were determined by Vickers microhardness measurements and uniaxial quasi-static tensile testing. Results and Discussion. It was established that, in all studied alloys, FSP leads to the formation of a recrystallized fine‑grained structure with predominantly equiaxed grain morphology. The best process stability and the most pronounced strengthening were achieved for aluminum bronze 89 Cu–9 Al–2 Mn and brass 63 Cu-37 Zn: microhardness, and ultimate tensile strength for 89 Cu–9 Al–2 Mn increased by 7, and 12%, respectively, and for 63 Cu-37 Zn increased by 22, and 4%, respectively, compared to the initial condition of the alloys. It was revealed that the higher thermal conductivity of the alloys necessitates an increase in axial tool force, which expands the shoulder‑affected zone and forms a wide stir zone. A pronounced grain size heterogeneity along the stir zone thickness was observed: in alloys with lower thermal conductivity under water cooling, the grain size near the root of the processed zone exceeded that near the top surface by a factor of up to 16, which is explained by differences in the rate of recrystallization arrest. Higher thermal conductivity promotes the formation of a more homogeneous grain structure, especially in the absence of forced water cooling.