Nowadays, consumer’s trend to functional foods containing prebiotic compounds is increasing. Prebiotics must be stable against food processing treatments, such as heat, Maillard reaction and low pH, so they reach the colon intact and cause stimulation of selective growth of colonic bacteria. So, the aim of this study is to extract the polysaccharide prebiotic of acorn and to investigate its stability against heat. The content of protein and ash of extracted prebiotic from acorn were 1.15 ±0.07 and 1.57 ±0.03, respectively. In this study acorn polysaccharide samples were heated in oven at 100 ?C and 180 ?C for 30 minutes after being dried with freeze dryer. The weight of samples was measured after heating. The weight of both samples had significant difference compared with control sample (p 0.05). Colorimetric results showed the lightness reduction of 180 ?C treatment in comparison with two other treatments, which is probably due to non-enzymatic browning reaction. The investigation of surface morphology of the particles by scanning electron microscope showed particles aggregation and filling holes of porous particles due to moisture absorption. The amounts of carbohydrate of control sample and 100?C and 180?C treatments with phenol-sulfuric method were 91.77±6.2, 88.55±2.09 and 69±7.07, respectively. Investigation of thermal analysis of samples by DSC showed similar process for all three samples. The endothermic peak around 271- 291?C is related to the crystalline transition and the exothermic peak around 292-332?C is related to the decomposition of acorn polysaccharides. The enthalpy of decomposition peak of the control sample and 100?C and 180?C treatments was 30.04, 21.03 and 41.22 (J/g) respectively. The TGA analysis showed that the thermal decomposition of control sample and 100?C and 180?C treatments was at 364.26, 360.97 and 356.36?C, respectively. The XRD analysis showed all three samples have semi-crystalline structure and 180?C treatment has higher crystallinity index in comparison with two other samples. HPLC analysis of three samples revealed that the polysaccharide derived from acorn is composed of raffinose, glucose and fructose. Solubility of control sample and 100?C and 180 ?C treatments at room temperature was 11.18 ±1.2, 19.31 ±0.21, and 5.34 ±1.2, respectively. The solubility of three samples was increased with temperature increasing from 25 to 60 ?C. Water holding capacity of control sample and 100?C and 180?C treatments was 5.92± 0.03, 5.05±0.06 and 7.31±0.21 (g water/g DM), respectively. Measured emulsion stability of control sample and 100?C and 180?C treatments was 71±1.41, 71.5±0.7 and 54±1.41 percent after 4 weeks. Antioxidant property of samples was measured by DPPH method and 180?C treatment was found to have higher antioxidant property. Lower carbohydrate content, solubility and emulsion stability of 180 ?C treatment as well as higher water holding capacity and antioxidant property of this treatment is related to non-enzymatic browning reaction and so the production of high molecular weight compounds with low solubility and high antioxidant property. The FTIR spectra of three samples showed the chemical stability of typical bands corresponding to polysaccharides in 100?C and 180?C treatments. Finally it can be concluded that the use of this polysaccharide in products with high temperature processing is possible. Keywords : Prebiotic, Stability, Acorn polysaccharide, Heat