The application of ultrasonic irradiation and ionic liquids (ILs) in the degradation of rice straw under different processes of pretreatment and enzymatic hydrolysis was investigated. Various substrates for enzymatic hydrolysis by cellulase with and without ultrasound were as follows: untreated rice-straw powder (RS); RS treated by ILs of 1-ethyl-3-methylimidazolium ethylsulfate and trihexyl (tetradecyl) phosphonium decanoate with ultrasound at 300 W/(40 kHz, 28 kHz); RS treated by IL of choline hydroxide ([Ch][OH]) with ultrasound at 300 W/ 40 kHz (CHRS). In ultrasound-mediated enzymatic hydrolysis, the yield of total reducing sugar (TRS) converted from CHRS was up to 96.22% at 240 min and was greater than that from the other substrates; the TRS yield for CHRS with ultrasound was 19.5% greater than that without irradiation. Lignocellulosic biomass pretreated with [Ch][OH] showed the highest efficiency among the tested ILs, and ultrasound can be applied effectively in rice-straw pretreatment and enzymatic hydrolysis. (C) 2014 Elsevier Ltd. All rights reserved.