The seeded crystal growth rate of calcium sulfate dihydrate was measured as a function of supersaturation in (\mathrm{NaCl}) electrolyte solutions from 0 to (6 m) at temperatures of (25,50,70), and (90^{\circ} \mathrm{C}). The growth followed a second-order parabolic rate law with activation energies greater than (53 \mathrm{~kJ} / \mathrm{mol}) which suggested the surface reaction as the rate-limiting step. It was observed that the rate constant and the activation energy are solution composition dependent. The rate constant increases with (\mathrm{NaCl}) concentration up to 3 molal and then begins to fall slightly. The activation energy dropped from (61 \mathrm{~kJ} / \mathrm{mol}) in the pure (\mathrm{Ca}-\mathrm{SO}{4}-) (\mathrm{H}{2} \mathrm{O}) system to (53 \mathrm{~kJ} / \mathrm{mol}) in (3.0 \mathrm{~m} \mathrm{NaCl}) solutions. The electrolyte effect was similar to the crystal solubility behavior in aqueous clectrolyte solutions resulting from the variation of the mean activity coefficient of the crystal with ionic strength. The rate constant is proportional to the crystal solubility and inversely proportional to the edge work or the interfacial tension as expected in the classic BCF model. 1994 Academic Press, Inc.