In this work, demulsification of water-in-crude oil emulsions by dielectrophoresis via applying a non-uniform electric field in a lab-scale cylindrical cell was studied. The stability of emulsions was assessed through monitoring the size distribution of water droplets at 0, 3, 6, and 24 hours after the preparation of emulsion. The effect of operating parameters including temperature, demulsifier concentration, water salinity, and time on the demulsification of water was investigated. Sodium dodecyl sulfate and sodium chloride were used as demulsifier and salt, respectively. The experiments were designed by response surface methodology (RSM) based on the central composite design (CCD). The operating parameters including voltage, temperature, demulsifier concentration, salinity of water, and separation time were optimized. The contours and 3-D response surfaces of water separation were acquired. A quadratic polynomial model, which was statistically highly significant (R2=0.9950, n=32), was provided by RSM to predict the amount of separated water. Comparison among the experimental and RSM-optimized values indicates a good agreement. The optimum amount of water separation was obtained at the voltage of 15 kV, temperature of 60 °C, demulsifier concentration of 123 ppm, salinity of water of 12260 ppm, and separation time of 12.4 minutes. At such conditions, the separation of water reached 98%. The results obviously show that the electric field can be used as an appropriate means for the breakage of W/O emulsions.