Today milk has a special effect in human societies as a valuable source of nutrition. Chemical safety is one of the most important issues that should be widely considered and evaluated. The process of food processing causes chemical changes in some of the ingredients in the food, including carbohydrates, proteins, fats and vitamins, and leads to the formation of toxic and hazardous compounds. These types of adverse chemical reactions are generated during the heating, storage, or other industrial processes, and are affected by the processing methods and the constituents of the food substance. During of thermal processing in order to produce dried milk, lactose and lysine react in maillard reaction and produce toxic and harmful compounds like furfural, hydroxymethylfurfural, and so on. In this research, various treatments with heating at different times and temperatures were performed to study the rate of maillard reaction and the effect of heating on functional properties during the levels production of dry milk powder from skim milk. The difference of treatments with each other during the heating period after the pasteurization step was at 75 ° C and the concentration at 60 ° C , so that 0, 30 and 60 minutes was used. Also, the control treatment, which was unheated, was isolated only when cooling after pasteurization and condensation step without heat treatment. To evaluate the effect of heating on the quality of dried milk powder, functional characteristics such as powder rehydration, viscosity, emulsifier properties, protein precipitation and density were evaluated in different treatments. To evaluate the progression of the maillard reaction during the production of dried milk powder, the amount of produced fluorescence compounds, the amount of free amine, and changes in the color of dried milk powder and reconstituted milk from the powder were measured. Reduction in quality of dried milk powder produced by the application of a severe thermal processing, was confirmed by measuring functional properties. Due to the use of the thermal processing after pasteurization and condensation step more than 30 minutes, the amount of denaturation and precipitation proteins was increased. This factor leads to increase viscosity, density and duration of powder rehydration, and decrease in the activity and stability of the emulsion. However, heating for 30 minutes improved the properties of emulsion and rehydration of the powder, and ultimately increased the quality of dried milk powder. Increase in amount of fluorescence compounds and colored compounds in dry milk powder and decrease in amount of free amine groups in dried milk powder indicates the progression of the maillard reaction due to the application of a severe thermal processing during the production of dried milk powder. However, the rate of progression of the maillard reaction is negligible, if it is heated for 30 minutes after condensation. Keywords: Maillard, Milk powder, Heat treatment, Free amine, Fluorescence