The effects of lactic acid concentration (LA) and spray drying conditions on stickiness of acidified skim milk powder (SMP), which impacts process efficiency and powder properties, were examined using a fully replicated 2^4-1 fractional factorial design. The wall deposition was significantly affected by LA, and yield was positively influenced by the drying temperature difference. Drying temperature difference significantly affected particle size, moisture content and water activity of acidified SMP. Particle size was also significantly influenced by nozzle airflow rate. Moisture content and water activity were significantly affected by LA, while glass transition temperature was only influenced by the outlet temperature.