The internal friction and Young's modulus of single crystals of copper were measured as a function of strain amplitude after they were subjected to various amounts of cold work and different annealing treatments. It was found that the position of the peak in the internal frictionversuscold‐work curve was dependent upon the strain amplitude of the measurement. No minimum in the Young's modulusversuscold‐work curve was found as contrasted with Lawson's result for polycrystalline copper. A minimum was found in the internal frictionversusannealing time curve, and a maximum was found in the corresponding Young's modulus curve. The results are semiquantitatively explained using a dislocation model.