It is necessary to drill micro holes in some hard brittle materials. Comparing with electro discharge machining, electrochemical machining and laser machining, the ultrasonic machining (USM) has unique advantages in hard brittle materials machining. The aim of this paper is to present experimental work that has been done in micro holes machining by micro USM. The main machining mechanisms of USM are discussed. It is pointed out that the contributions of each mechanism to material removal rate are different in different cases. By using micro USM with workpiece vibration and tool feeding in constant rate, the experiments of micro holes machining are carried out and the process laws of tool wear are studied. Some phenomena are found and the causation of causing these phenomena is analyzed. A Ø13μm micro hole is obtained.