In this study, rice straw (RS) was liquefied by ethylene carbonate (EC) using H₂SO₄ as a catalyst. The effects of various process conditions on the liquefaction characteristics were investigated by FT-IR and residue content analysis. The results show that cellulose and lignin are degraded during the liquefaction process and large amounts of groups are generated. In addition, it is difficult to effectively liquefy RS by using EC alone as the liquefying agent without other additives. Compared to water addition on liquefaction, the residue content can be significantly reduced up to 30% by adding H₂O₂. It has also been proved that the liquor ratio (RS/EC, w/v) of 1∶5 with H₂O₂ as an additive at 145℃ for liquefaction time of 60 min in the presence of H₂SO₄ can accelerate the liquefaction process and high liquefaction yield can be obtained.