Using Field Assisted Sintering Technique/Spark Plasma Sintering the effect of heating rate on the sintering of zinc oxide at a temperature of 400 degrees C has been investigated. For the highest heating rate of 100 degrees C/min, relative density larger than 95% was achieved whereas at low heating rates only little shrinkage occurred. Hardness measurements, Transmission Electron Microscopy, and impedance spectroscopy revealed clear differences between heating rates. It was found that residual water is responsible for this behavior, enhancing particle rearrangement and diffusion kinetics.