In this study, ultrasonic field was applied during potassium hydroxide (KOH) pretreatment of wheat straw (WS). Three concentrations of KOH (2%, 4%, and 6%) were tested during pretreatment. The results showed that there was a significant influence of the ultrasonic assisted KOH pretreatment (KOHUpt) on physiochemical characteristics of WS during pretreatment as well as on digester performance. The pretreatment time was optimized to 36 h for all KOH concentrations. The highest total volatile fatty acid (TVFA) productions (3189 mg.L-1) from 6% KOHUpt samples were observed. Similarly, the SEM analysis and FTIR observation revealed that KOHUpt effectively disrupted the physical morphology of WS and successful breaking of lignin and hemicellulose linkage between carboxyl groups. Moreover, the highest biogasification (555 ml.(g VSloaded)(-)(1)) and biomethane productions (282 ml.(g VSloaded)(-)(1))( )from 4%KOHUpt digesters, with 69% of biodegradability, indicated significant availability of organic matter from KOHUpt. The R-2 values (0.993-0.998) in Modified Gompertz Model indicated that the model was feasible to predict methane yield for this study. Similarly, the B-o values for 4%KOHUpt (283.30 +/- 2.74 ml.(g VSloaded)(-)(1)) were also in agreement to the experimental methane yield. These results suggested that ultrasonic addition during KOH pretreatment of WS can effectively increase the organic yield during pretreatment. Moreover, the increase in methane production from 4% H-Upt suggested that digester performance can be improved with lower KOH concentrations using this pretreatment. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.