Deproteinized whey (DPW) is obtained as a permeate fraction during ultrafiltration of whey and generally contains a minimum of 76% (db) lactose. It is further processed into a non-hygroscopic and free-flowing DPW powder by crystallization and spray drying. The DPW may undergo changes such as caking and Maillard browning during storage. The aim of this study was to investigate the effect of different levels of lactic acid (LA) and galactose (GA) on the physical, chemical, and thermal properties of DPW powders. Two lots of concentrated permeate with total solids of ~77% were procured from a commercial manufacturer. The total solids were adjusted to 45% TS and was divided into 9 subsamples with treatment combinations of high, medium, low levels of lactic acid by adjusting the pH to 5.0 by adding 0.2% lactic acid, pH 5.55 with no addition and pH 6.10 by adding 2% NaOH and galactose (0, 0.15, and 0.30%) as per the experimental design. The DPW powders were spray dried in a lab-scale spray dryer with inlet temperature 180°C and the outlet air temperature 83–88°C. The water activity (a_w) and L* values of the powders immediately after spray drying were not significantly different (P > 0.05) and was in the range 0.074 to 0.098 and 91.89 to 92.81, respectively. It was observed that the pH of the powders decreased with increase in lactic acid contents. The pH of low LA and high LA powder were found to be 6.60 and 5.78, respectively. The titratable acidity also increased with increasing lactic acid content and ranged from 0.03 to 0.08% LA. The hygroscopicity values were not significantly different (P > 0.05) for the powders and were determined to be in the range 7.8 to 11.3% and the caking tendency of the powders ranged from 97.73 to 98.55%. The thermal properties of the stored DPW powders were determined with differential scanning calorimetry and a dehydration endothermic peak at around 142°C was observed which represented loss of crystalline water. Overall, the DPW powders did not show any significant difference for all the treatment combinations immediately after production.