The pretreatment of lignocellulosic biomass in biorefineries is a very promising path for their conversion into value-added products. However, development of sustainable pretreatment for efficient conversion of lignocellulosic biomass into value-added materials is still an emergent and challenging field. Herein, a new direction for the utilization of deep eutectic solvent (DES) pretreatment of lignocellulosic biomass in the fabrication of compression-molded biocomposite panels was studied. The impact of untreated and DES-treated fibers of three types of lignocellulosic waste-corn stover (CS), peanut shell powder (PSP), and sugarcane bagasse (SCB)-on the properties of biocomposite panels using urea-formaldehyde binder was investigated. Cellulose-rich fiber (CRF) was extracted by pretreating lignocellulosic materials with choline chloride and glycerol-based synthesized DES under mild operating conditions, and high solids loading and mechanical and water absorption properties of the biocomposite board prepared from untreated and DES-treated fibers were measured. The effect of DES pretreatment on the properties of lignocellulosic fibers was evaluated using Fourier transform infrared spectroscopy (FTIR), lignocellulosic compositional analysis (LCA), thermogravimetric analysis (TGA), and X-ray diffraction analysis (XRD). These analyses revealed that cellulosic content and thermal stability of all DES-treated fibers improved compared to untreated samples. The biocomposite board made from DES-treated fibers had higher strength and modulus than the untreated composite board, as determined by the three-point bending test. Specifically, the modulus of rupture (MOR) and modulus of elasticity (MOE) of SCB biocomposite panels increased from 26.15 MPa and 1564.65 MPa to 31.28 MPa and 1871.74 MPa in DES-treated panels, respectively. These findings suggest that the novel DES-based pretreatment could be a promising sustainable processing strategy for converting agro-industrial waste into CRF to fabricate wood-composite panels with a wide range of furniture and construction applications. (C) 2022 Elsevier B.V. All rights reserved.