Polysaccharides are a mixture of biological polymers with unique functional properties such as thickening, stabilization, emulsion formation and gel formation, which have vast applications for the food, pharmaceutical, medical, cosmetic, and oil wells. One of the materials that can be used to extract polysaccharides is Oleaster that called Elaeagnus angustifolia L. Oleaster is a tree plant of the Elaeagnaceae family. The aim of this research was to optimize the polysaccharides extraction of oleaster fruit and then to investigate the physicochemical and functional characteristics of extracted polysaccharide. Therefore, RSM was used in order to optimize the polysaccharide extraction of oleaster. Four factors of temperature, water to dry matter ratio, time and alcohol ratio were considered as variables and the purity of extracted polysaccharide was considered as the response. Optimization of polysaccharide extraction from full grain oleaster showed that all variables alone or by interaction with other variables had effect on the purity of polysaccharide extraction. The results showed that the temperature 60 ( ? C), water to dry matter ratio 1: 53 (W/V), time 5 (h) and alcohol ratio 2.9 (V/V) were the best conditions for achieving the highest purity of extracted polysaccharide. The purity of extracted polysaccharide under optimum conditions was 65%. The properties of polysaccharide extracted under optimum conditions were evaluated. Measuring the emulsifying stability showed that the extracted polysaccharide has the potential of emulsion formation with high stability. This polysaccharide is able to form and maintain different emulsions with different percentages of oil. However, the foamability was not observed in this polycsaccharide. Also, the solubility percentage of polysaccharide powder was high and the solubility increased from 63% to 72% with increasing temperature from 30 to 90 ( ? C). However, with increasing the temperature from 30 to 90 ° C, the water absorption was decreased from 0.6 to 0.25 (g/g). This indicates the effect of heat on the structure and the amount of water absorption of extracted polysaccharide. The results obtained from the infrared spectroscopy showed that the highest extracted composition is polysaccharide. The x-ray diffraction pattern of extracted polysaccharide showed its semi-crystalline structure. Keywords: Elaeagnus angustifolia, Polysaccharide, Functional Properties, Oleaster.