This paper reports a study of rotary electro-discharge machining (with a metal bonded diamond wheel) of polycrystalline diamond (PCD). In this type of rotary EDM, the electro-erosion is combined with the grinding action. Significant improvements in material removal rates and surface quality have been observed with rotary EDM of PCD material. An investigation of gap pulse characteristics reveals unique features that may lead to a better understanding of the material removal mechanism and therefore process improvement.