Control of supersaturation in a 1-L continuous cooling KCl crystallizer was investigated. The supersaturation was determined from on-line measurements of the density and temperature of clear liquor samples. A cascade control scheme was used to control the supersaturation through the manipulation of the co-saturated feed temperature set-point while maintaining the crystallizer temperature at 303.2 K. Experimental results showed that due to the suppression of spontaneous nuclearion, a decrease in the measured supersaturation resulted in a 23% increase in the mean crystal size and a 12% decrease in the amount of NaCl impurity in the KCl crystals..