Soy protein has a high nutritional value and is effective in the prevention and treatment of diseases such as heart disease, some cancers and osteoporosis. Some efforts has been done to produce dairy products including milk fortified with soy protein. To the best of these products with high protein density, should be prevented from being deposited in protein and minerals and also should have low viscosity to be easier to use. The color is the other parameter tha affect product acceptance and measuring electric conductivity and average particle size give some information about reactions in the mixture. In this study, Physicochemical properties of milk that fortified with soy protein isolates that had been sustained by the Arabic gum was studied. Mixture design by using of Design Expert software give us 20 different formulations including skim milk, soy protein isolate, Arabic gum and deionized water. In order to prepare the formula, at first soy protein isolate, arabic gum and a little deionized water were mixed and was hydrated for 30 minutes in a water bath with 80ْ C, then Skim milk powder was added and reach to the exact weight with deionized water, formulas were homogenized by two-stage pressure of 200 bar, and pasteurized with plate pasteurizator at 80ْ C and were kept at 4ْ C.The viscosity, sedimentation, and L and b parameters of color of these 20 formulas were measured at 1,8,15 and 22 days after pasteurization. Design Expert software was used for data modeling. Then distribution of the particle size of the formulas with the least, average and maximum amount of precipitation, were studied. For oral consumption or eating of this product, it is necessary to improve product taste; So one of the best formulas with the least amount of precipitation were choosed and After adding different flavors, sensory characteristics were evaluated by the evaluators and obtained data were analysed with the SAS software and comparing of the means was performed by LSD test. Modeling data showed that effect of component on viscosity and quantity of sedimentation were well adjusted by Special cubic and Quadratic model respectively and the best proposed model for conductivity and the L and b parameters were linear model. study of model after one day maintaining at 4ْ C showed that mixture in areas with high concentrations of skim milk and low concentrations of soy protein isolate had relatively low viscosity and at low concentrations of skim milk powder, increasing soy protein isolate, caused increasing the viscosity dramatically.Amount of precipitation was fixed and low in relatively wide areas and in the concentration range of more than 0.35% Arabic gum, decreased with increasing concentration of skim milk powder and also decreased by increasing soy protein isolate when Arabic gum were decreasing. Conductivity, decreased with increasing of Arabic gum and soy protein isolate and increased with increasing of skim milk powder. Increasing in Arabic gum caused increasing in L parameter and decreasing in b parameter; Increasing in skim milk caused increasing in L and b parameters but increasing of prameter were a little and increasing in soy protein isolate caused decreasing in L parameter and increasing in b parameter. Study showed that the distribution of particle size is effective on the amount of precipitation. Sensory test results indicated a significant positive effect of adding cocoa and coffee on smell and overall aceptance compared with the addition of vanilla alone in formulas that fortified by soy protein isolate(p=0/05). Keywords: Protein-protein interactions, Protein-polysaccharide interactions, Soy protein, Fortified milk, Physicochemical properties, Sensory characteristics.