The precipitates responsible for magnetic age hardening of a Co3.8Cu0.9Fe0.5Ce alloy have been directly observed by transmission electron microscopy. The precipitates are coherent, plate shaped disks which possess the rhombohedral Co17Ce2structure. They form in a  plate normal orientation and cluster in staggered rows at from the  axis. The development of precipitate microstructure has been examined in quenched, optimally aged, and overaged alloys. Direct evidence for interaction between the precipitate particles and magnetic domain walls has also been obtained. Among the recently developed Co5R based permanent magnets, the Cu containing alloys developed by Nesbitt et al. are of particular interest. These alloys are age hardenable; i.e., their magnetic properties may be improved and controlled by heat treatment. Previous work has revealed that their high coercivities may be attributed to the pinning of domain walls rather than to the nucleation of reverse domains. This report contains a description of some results obtained during an investigation of the alloy structures by transmission electron microscopy. We present direct evidence for the existence of coherent precipitates as well as for the existence of a pinning interaction between magnetic domain walls and the precipitate particles.