Abstract: The influences of water-leaching and different concentration acid-leaching pretreatments on physicochemical properties and steam gasification reaction characteristics of rice straw (RS) were investigated in a laboratory fixed-bed reactor. The results show that after water-leaching, the potassium and sodium in RS are removed by 90.5% and 82.1%, respectively, and after acid-leaching, the removal of potassium from RS reaches to 99.2%, and the removal efficiency of sodium with acids is between 84.6% and 92.3%. Acid leaching does not change the main component content of RS, but destroys the microscopic structures of RS. The order of different concentration acid-treated RSs with respect to the three indexes including pore volume, pore diameter distribution and specific surface area is: all water-leached RS > 3% sulfuric acid-treated RS > raw RS > 7% sulfuric acid-treated RS > 10% sulfuric acid-treated RS. As the concentration of various pretreatment acids is 3%, the sulfuric acid-treated RS has the largest values of the three indexes and the phosphoric acid-treated RS has the smallest values of the three indexes. The steam gasification results show that potassium, sodium and abundant pore structure all can promote hydrogen generation, and the effects of potassium and sodium on gasification process are significantly stronger than pore structure. The H₂ and CO₂ instantaneous release concentration for water-leached RS is higher than that for acid-treated RS during gasification; however, it is contrary to CO and CH₄. When the four acids concentration is 3%, there is a positive correlation between H₂ and CO₂ instantaneous release concentration and the pore diameter distribution; and there is a negative correlation between CO and CH₄ instantaneous release concentration and the pore diameter distribution. The more abundant the pore, the faster the gasification rate. Though deashing pretreatment decreases the H₂ production, it increases the calorific value of gasification gas.