Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 °C, 100 MPa and oxygen fugacity (fO₂) buffered at approaching Ni–NiO (NNO). Partition coefficients of Cu (D_Cu = c_fluid/c_melt) were varied with different alumina/alkali mole ratios [Al₂O₃/(Na₂O + K₂O), abbreviated as Al/Alk], Na/K mole ratios, and SiO₂ mole contents. The D_Cu increased from 1.28 ± 0.01 to 22.18 ± 0.22 with the increase of Al/Alk mole ratios (ranging from 0.64 to 1.20) and Na/K mole ratios (ranging from 0.58 to 2.56). The experimental results also showed that D_Cu was positively correlated with the HCl concentration of the starting fluid. The D_Cu was independent of the SiO₂ mole content in the range of SiO₂ content considered. No D_Cu value was less than 1 in our experiments at 850 °C and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatic-hydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than the melt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl⁻ fluid.