During recent decades, ultrasonic pretreatment has attracted considerable attention as an effective mechanical method for improving sludge solubilization and enhancing anaerobic digestion performance. This technique is considered environmentally friendly due to its operational stability, compact system design, and efficient process performance. In the present study, ultrasonic pretreatment was applied to giant reed, a lignocellulosic biomass, to evaluate its potential for enhancing biogas production during anaerobic co-digestion with chicken manure. Different sonication times (5, 10, and 15 min) and ultrasonic power levels (240, 480, and 720 W) were investigated at a low frequency of 20 kHz. The efficiency of the process was assessed based on biogas yield and methane content under mesophilic batch digestion conditions. Results showed that ultrasonic pretreatment significantly influenced digestion performance. The highest biogas yield was 239 mL g⁻¹ VS, with a methane content of 122 mL g⁻¹ VS, corresponding to approximately 51% of the total biogas, at an applied power of 240 W and 10 min. At a sonication power of 480 W and 15 min, the biogas yield reached approximately 234 mL g⁻¹ VS, while the methane content attained its highest value of 132 mL g⁻¹ VS, representing approximately 56.4% of the total biogas produced. Ultrasonic pretreatment increased the methane content from 34 to 132 mL CH₄/g VS, corresponding to an increase of approximately 288.2% compared with the untreated sample. The findings indicate that moderate ultrasonic energy with suitable exposure time improves substrate accessibility and biomass degradation without negatively affecting digestion efficiency. Response surface methodology further confirmed that sonication time and ultrasonic power strongly affected methane production, with optimum performance observed at 15 min and 480 W.