The geochemical cycling of copper in the hydrosphere and soil environments primarily involves the transport of Cu from rocks to rivers via weathering. Understanding the factors controlling Cu isotope fractionation during weathering is crucial for the purpose of using Cu isotopes as a tracer of geochemical cycling. Here, we performed acid-leaching experiments on natural basalts (BHVO-2 and GBW07105) and chalcopyrite in Erlenmeyer flasks at T = 25 ℃ and different pH values (0.3 and 2). Our results reveal substantial Cu isotope fractionations (Δ65Cusolution-initial) between leachates (Cusolution) and starting materials (Cuinitial). The leachates released from GBW07105 and chalcopyrite are consistently enriched in heavier Cu isotopes relative to the starting materials at pH=2. However, theδ65Cusolution val- ues decrease to about-0.6‰first, then increase to>0 for BHVO-2 at pH=2 and GBW07105 at pH= 0.3. Our results indicate that leaching of natural rocks by acidic liquids can produce both positive and negative Cu isotope fractionation, depending on pH values and the types of minerals in starting materi- als. X-ray power diffraction analysis (XRD) patterns reveal similar mineral assemblages between start- ing basalts and residues after each reaction round. The most likely mechanisms responsible for such Cu isotope fractionation are the relative rates of Cu oxidation at the surface and Cu release into solution, and the sequence of mineral dissolution. Our study represents an important step for future studies to use Cu isotopes to explain Cu isotopic variations in natural rocks and waters.