In recent years, the addition of the various nanoparticles in dielectric of EDM process has been considered in order to improve the material removal rate (MRR) and surface roughness. In this regard, the effects of the addition of metal oxide nanoparticles including Cu, Al, Al2O3, C, Si, SiC, Gr and W, in different dielectric such as deionized water, kerosene, mineral oil and silicon oil, are surveyed. The results illustrate that the parameters such as the density, particle size, particle concentration and electrical and thermal conductivity of the nanoparticles can be affected on the process performance. ZnO is one of metal oxides which has high thermal and electrical conductivity so that it can improve the performance of EDM process. In this paper, the effects of the mass concentration of ZnO particle (1 to 4 gr)in dielectric of EDM process and the variation of peak current (between 6A to 24 A) on MRR and surface roughness in AISI 1045، AISI 4140, AISI D3 steels are investigated. The studies are done in two classifications that are including the rough and the finish machining. In rough machining, the results illustrate that the mass concentration 4 gram of ZnO nanoparticle mass increase the MRR values up to %10, %50 and %40, in AISI1045, AISI4140 and AISID3, respectively. Although, In finish machining (with the peak current 6A), the results are shown that the surface roughness in finishing in the AISI 4140 and AISI D3 was significantly improved, but the improvement of AISI 1045 is just %10.