The present study assesses imitative ability in chimpanzees and human children. A direct comparison of these two species was conducted in an object-manipulation task. The subjects were required to copy the model stack by stacking colored blocks in the same order as the model. Four juvenile/adolescent chimpanzees failed to copy the model stack even after a long training-period. Two adult chimpanzees eventually learned to copy the model stack of two blocks. However, they failed to copy the model of three blocks, and analysis of their stacking patterns revealed that they only focused on the color of the top block in the model. Human children started to copy the model of two blocks when they were two years of age and gradually increased the number of successfully copied blocks. The results from both chimpanzees and humans are discussed in terms of the social intelligence involved in object manipulation.