THIS PAPER PRESENTS THE WEAR CHARACTERISTICS OF DIAMOND TOOLS WITH DIFFERENT CRYSTALLOGRAPHIC ORIENTATIONS IN ULTRA-PRECISION MACHINING OF COPPER. IT IS FOUND THAT A SINGLE DIAMOND TOOL WITH ORIENTATION (100) AT BOTH RAKE AND FLANK FACES HAS BETTER WEAR RESISTANCE THAN A DIAMOND TOOL WITH CRYSTAL ORIENTATION (110) AT THE RAKE FACE AND (100) AT THE FLANK FACE. AN ANALYSIS OF THE ATOMIC WEAR PHENOMENA OF DIAMOND TOOL, ALSO INDICATES THAT THE WEAR RESISTANCE OF DIAMOND IN THE DIRECTION OPPOSITE TO THE CHIP FLOW DIRECTION STRONGLY DEPENDS ON THE AMOUNT OF CHEMICAL BONDS PER UNIT AREA BETWEEN THESE CRYSTAL PLANES.