Crystallization of lactose in supersaturated solution is influenced by factors like cooling rate, the presence of impurities, pH, the degree of supersaturation, and agitator speed. This study was focused on the influence of different cooling rates on crystallization of lactose in supersaturated deproteinized whey (DPW). DPW powder composed of 78.3% lactose, 10% minerals, and 6.3% proteins was reconstituted to 60% (wt/wt) total solids at 80°C for 2 h under constant stirring to ensure complete solubilization of lactose. Supersaturated DPW was then transferred to double jacked crystallizer connected to a programmable water bath and cooled from 80°C to 60°C in 40 min followed by one of the cooling rates. Three cooling rates 0.04(slow), 0.06(medium), and 0.08 (fast) °C/minute from 60°C to 20°C were studied as part of the experimental design and were all done in duplicate. The effect of cooling rates on the quality of the lactose crystals in terms of lactose yield, protein, and mineral percent in dried lactose, and mean particle chord lengths were studied. Lactose yield was measured by weighing dried lactose obtained from crystal slurry that was centrifuged, washed thrice and dried at 60°C for 14 h. Lactose yield for slow, medium, and fast cooling rates were 74 ± 0, 71.5 ± 3.54, and 72.5 ± 0.71%. The amount of the proteins in dried lactose crystals were 0.77 ± 0.06,0.72 ± 0.04, and 0.68 ± 0.06%; the and amount of the minerals were 1.32 ± 0.02,1.38 ± 0.03, and 1.46 ± 0.18% for slow, medium and fast cooling rates respectively. Mean chord lengths measured at the end of crystallization using focused beam reflectance measurement (FBRM) for slow, medium and fast cooling rates were 33.22 ± 2.43, 30.28 ± 5.13, 27.05 ± 3.04 µm, respectively. Lactose yield, protein and mineral percent, and final mean particle chord lengths showed no significant difference (P > 0.05) between the 3 cooling rates studied. This study successfully investigated the effect of cooling rate on crystallization to reduce its time.