Micro Electro Discharge Machining (micro-EDM) is widely used for producing different types of micro features and micro components. Tool wear rate (TWR) is an important factor that affects the accuracy of machining as well as the productivity of micro-EDM process. This study examines the effects of process parameters and the use of Maghemite (ý-Fe2O3) nano-powder mixed dielectric medium on tool wear rate when micro-EDM Co-Cr-Mo. A Copper electrode with 300 µm diameter and positive polarity was used to evaluate the machining process by focusing on TWR. Two different concentrations of nano-powder (i.e., 2 g/l and 4 g/l) were added to the dielectric. Results showed that increasing the discharge current and voltage leads to a corresponding increase in TWR, while the presence of ý-Fe2O3 nano-powder in the dielectric liquid decreases TWR. Mixed micro-EDM with 2 g/l of nano-powder achieved a lower TWR.