Abstract: Rapeseed cake, a by-product of oil processing, exhibits limited feed value due to its high content of antinutritional factors and poor palatability. To achieve high-value utilization of this resource while integrating environmental and economic benefits, crude cellulose was extracted from rapeseed cake and converted into nanocellulose via hydrogen peroxide-assisted TEMPO-mediated oxidation. A composite aerogel of rapeseed cake nanocellulose and graphene (RCN/G) was then prepared through a sol-gel process followed by freeze-drying. The aerogel was characterized using zeta potential analysis, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and N₂ adsorption-desorption (BET) analysis. Static adsorption experiments were conducted to evaluate the effects of nanocellulose concentration, solution pH, temperature, and Na⁺ concentration on the adsorption of methylene blue (MB). The results indicate that with the progression of the processing steps, the zeta potential of the rapeseed cake cellulose surface decreases from −12 mV to −41 mV. The composite aerogel exhibits a specific surface area of approximately 30.46 m²·g⁻¹ and a porosity of 77.03%. The MB adsorption behavior of the composite aerogel is significantly affected by Na⁺ concentration. Moreover, increasing the nanocellulose concentration markedly enhances the adsorption capacity by providing more accessible adsorption sites, with the capacity for MB stabilizing at approximately 9 mg·g⁻¹. The adsorption process follows the pseudo-second-order kinetic model and is primarily driven by chemisorption. The findings demonstrate that the rapeseed cake nanocellulose/graphene (RCN/G) composite aerogel has potential for application in dye wastewater treatment.