A model is presented to study the steady and transient state responses of the system during startup and sudden load changes/disturbances of the Multi-effect Mechanical Vapour Compression (ME-MVC) desalination system. Some of the main dependent parameters like the compressor work, and the mass flow rate of distilled water against the independent parameters like the evaporation side pressure and the water inlet temperature have been studied. Also, the Performance Ratio (PR) and the heat transfer area dependency on the number of effects and Top Brine Temperature (TBT) have been studied. The material and energy balance equations for the feed, product and brine flow for each effect have been written and then solved simultaneously to obtain the time-dependent parameters under various transients. The effects of a step change in feed flow and temperature with respect to brine salinity and product flow rate, etc. have also been studied. Copyright © 2006 Inderscience Enterprises Ltd.