Magnesium stearate (MgSt) is widely used as an effective lubricant in the pharmaceutical industry for tablet formulation. This widespread application is due to its low price and very high lubricating ability. It is nonsoluble in water because of its highly apolar molecular structure and hydrophobic nature, and its good chemical and physical properties make it a good candidate for being used as an emulsifier and anti sticking agent. The aim of this work was to separate sodium sulfate from MgSt aqueous slurry which exists as an impurity at the final stage of industrial production of MgSt. By separating sodium sulfate it was possible to recover some of excess sodium hydroxide used at the first stage of MgSt production and also avoid using a large amount of water used in the common process used in industry for sodium sulfate removal. For this purpose an electrodialysis cell was designed and built and batch mode of electrodialysis process was implemented. At the first step some preliminary experiments were done to investigate the influences of some parameters including applied voltage, MgSt concentration, middle compartment stirrer speed and NaOH initial concentration in cathodic chamber on sodium ions recovery, energy consumption and sodium ions traort flux. High sodium recovery (about 90%) was obtained at 15%wt MgSt, voltage of 20 volt and stirrer speed of 250 rpm which proved that implemented method can be considered as proper candidate for salt recovery from MgSt slurry. The results indicated that increasing voltage in ED cell enhanced the separation of sodium ions. Also using higher MgSt concentration led to decrease of sodium recovery which showed that this system is more suitable for low feed concentrations. By increasing feed compartment stirrer speed from 250 to 500 rpm, formation of very high turbulence regime in feed chamber prevented ions from migrating from diluate to concentrate compartment which led to lower ion traort flux and decreasing sodium ions recovery. Response surface method (RSM) was used to investigate the effects of operating parameters on sodium ions recovery and specific power consumption. Five levels were selected for the operaing parameters including voltage (in range of 5-25 volts), MgSt concentration (in range of 10-60 wt %), stirrer speed (in range of 200-600 rpm) and time (in range of 20-180 min) to design the experiments. In this part of the work, initial concentration of NaOH and H 2 SO 4 in cathodic and anodic chambers were adjusted at 0.5 M. The quadratic models established for sodium recovery and energy consumption in terms of operating parameters with determination coefficient R 2 of 0.9276 and 0.9243 respectively, indicated that offered response surface models are helpful to describe the sodium ions recovery and specific power consumption. Analysis of variance (ANOVA) showed that, voltage and time were the most influent parameters on the sodium ions recovey with Prob F less than 0.0001 whereas stirrer speed had no significiant effect with Prob F of 0.3595. Also voltage and middle compartment stirrer speed were the most influent variables on the specific power consumption with F-value of 132.9 and 23.37 and Prob F of less than 0.0001 and 0.0002 respectively. Keywords: Magnesium stearate; Electrodialysis; Separation; Response surface method