Nuclear envelope breakdown is a critical step in the cell cycle of higher eukaryotes. Although integral membrane proteins associated with the nuclear membrane have been observed to disperse into the endoplasmic reticulum at mitosis, the mechanisms involved in this reorganization remain to be fully elucidated. Here, using Xenopus extracts, we report a role for the COPI coatomer complex in nuclear envelope breakdown, implicating vesiculation as an important step. We have found that a nuclear pore protein, Nup153, plays a critical role in directing COPI to the nuclear membrane at mitosis and that this event provides feedback to other aspects of nuclear disassembly. These results provide insight into how key steps in nuclear division are orchestrated.