This paper presents the results of micro ultrasonic machining using oil based abrasive slurry. An in-house built experimental setup was used to conduct designed experiments. The influence of process parameters such as slurry medium, slurry concentration, and abrasive particle size on the performance of micro USM Material Removal Rate (MRR) and Surface Roughness (SR) is reported. It is evident from the experimental study that machining with water based slurry is suitable only for finer particles sizes with higher concentration or medium particles sizes with medium concentration or coarser particle sizes with lower particles where as machining with oil based slurry is always suitable for all the particle sizes with low concentration. Further the study reveals that machining with oil based slurry gives good surface finish compared to the water based slurry. Good surface finish is given by machining with the finer particles whereas machining with coarser grains gives poor surface finish.