Monel 400 alloys are used in various fields such as aerospace industries, marine industries, etc. It is very difficult to machine Monel 400 alloys using conventional machine tools. The Electrochemical Machining (ECM), an advanced manufacturing process, is a natural choice for machining Monel 400 alloys. The present work is carried out to investigate the influence of ECM process parameters, such as applied voltage (V), inter electrode gap (IEG) and electrolyte concentration (EC), on material removal rate (MRR) and surface roughness (Ra) during machining Monel 400 alloys. An aqueous sodium chloride (NaCl) is used as a basic electrolyte in the electrochemical machining of Monel 400 alloys. The experimental strategy is based on a response surface methodology. The effects of process parameters as well as their interactions are investigated and the process parameters are optimized through the desirability function of the response surface methodology. The microstructure of the Monel 400 alloys specimen, machined with ECM, is studied to understand the effect of electrolyte and other parameters during the machining. © 2014 Jordan Journal of Mechanical and Industrial Engineering.