Grey oyster mushroom (Pleurotus sajor-caju (Fr.) Singer) is a popular edible mushroom in Thailand due to its high nutritional and medicinal benefits. This study aims to study the effects of temperature (100-140 °C), pressure (4-7 bar), and extraction time (20-60 min) on the extraction crude polysaccharides with environmentally friendly pressurized hot water. The extraction condition was optimized by the maximize yield using response surface method based on a central composite design (CCD). The temperature was the main effect on the increase of extracted yield. The optimum extraction condition was 140 °C, 10 bar, and 26.79 min with a corresponding yield of 31.31±2.55%. Under these conditions, the total phenolic content of crude polysaccharides was 401±8.24 mg GAE/g dry mushroom. In addition, the total glucan content was indicated as 34.50 ±1.79 g/100 g dry mushroom, which separated as 32.47±1.95 mg/100 g of β-glucans and 2.04±0.98 mg/100 g of a-glucans.