The miniaturization of parts and components plays an important role in today’s economy, enabling the design and the production of new and highly sophisticated systems in various industrial fields, such as medical, bio-chemistry, automotive and telecommunications. Micro holes are widely used in micro-electromechanical systems (MEMS) serving as channels or nozzles to connect two micro-features. Micro Electrical Discharge Machining (micro-EDM) and micro laser ablation are both thermal processes used to realize micro holes. As regards micro-EDM technology, material is removed by a series of rapid electric spark discharges between the cutting tool (electrode) and the workpiece. It is able to machine complex micro parts of only conductive materials that traditional processes are unable to create. In fact, being a contact-less process, there are very small machining forces between the electrode and the workpiece. This makes it easy to produce micro parts without distortion due to physical forces. EDM is an ideal process for obtaining burr-free micro-size machined parts with high aspect ratio using different conductive materials. In fact, many factors can affect the performance of the EDM process; these factors can be related to the process parameters (such as voltage, peak current, pulse duration, sparking gap, etc.) or to the system (such as type of dielectric fluid, tool properties, chemical and physical material properties). Unfortunately the effect of micro-EDM process parameters on the final output is partially unknown and it has to be clarified. Aim of this work is to investigate the effects of several types of electrode (different materials and shapes) in drilling micro-holes on stainless steel, titanium and brass using micro-EDM technology. The workpiece plates having a thickness equal to 0.5 mm and 1 mm were taken into account and the diameter of holes was 0.3 mm. The characterization of holes was conducted considering both the process performance (machining time and tool wear rate) and the geometrical and dimensional properties (overcut and taper rate).