A theoretical analysis of the rate of anhydrous CaSO4-scale deposition in sea-water evaporators is presented under the premise that the deposition may be regarded as a simple crystallization process of anhydrous CaSO4 taking place on a heating surface superheated above the saturation temperature of evaporator liquid. Discussion is presented in Section 1 to show that the above simplified treatment is applicable to evaporation of sea water seeded with fine anhydrous CaSO4 crystals to suppress scale formation.By this simplified treatment, the surface temperature, tw, of the heating surface in contact with the evaporator liquid is shown to be an essentially important factor to determine the rate of scale formation, which, therefore, depends on the question of which side of the heat-transfer wall has greater resistance to heat flow, -the liquid side or the vapor condensing side.Equations (2) and (3) give the rate of scale formation and the thickness of the scale, respectively. When the equations are employed to analyze the published data on anhydrous-CaSO4-scale formation in sea-water evaporators, a reasonable agreement is obtained between the measured data and the calculated values as shown in Fig. 3. Possible explanations for the deviation of the data from the theory are discussed. The data and the calculations are summarized in Table 1.Based on this agreement, the influence of some important variables on the rate of scale formation is discussed, where the variables cover ce/cs, tw, tL and u. Some numerical examples are given for these variables, showing that the theory can predict the actual scale formation reasonably well.