Cu isotopic fractionation occurs in plant, the fractionation direction andmagnitudewould vary between different plant organs (i.e., root and stem) as well as different plant tissues (i.e., xylemand phloem). Remobilization of Cu associated with plant senescencewas found to have a considerable effect on Cu isotopic fractionation within the plant, and the fractionation factor was found to change with the degree of remobilization. Overall, the results show that the Cu isotopic composition is useful as a tracer for probing the mechanisms of Cu translocation and retranslocation between soil and plants, and within plants.