This study pertains to dynamic simulation for the analysis of start-up characteristics of multi-stage flash (MSF) desalination plants using a mathematical modeling. A simulation program was developed to predict dynamic behaviour of MSF plants which can be used either to design or to simulate actual plant operation. Stage-by-stage calculations have been carried out to predict the dynamic behaviour of the plant. Variations of all the thermodynamic properties with temperature and salinity are considered. Start-up characteristics, i.e., time variation of flashing brine flow rate, heating steam flow rate, stage brine level, stage temperature, stage pressure, stage-wise flashing rates, etc., are calculated using the coupled Runge--Kutta method. The predictions are compared with the start-up data obtained from the 425m³/d MSF plant at the Desalination Division, BARC, Mumbai (India). The simulated data are very close in agreement with the actual data.