The current study aimed to optimize Cd(II) removal from aqueous solutions by a composite adsorbent (BCB) prepared from Alternanthera philoxeroides (AP) biochar (BC) and bentonite (BE) using response surface methodology (RSM). The results showed that the loading of BE did not significantly change the microstructure of BC but increased the number of functional groups. The X-ray diffraction (XRD) analysis showed that precipitation was the primary mechanism of Cd(II) adsorption. The adsorption behavior for Cd(II) fitted the Freundlich model. The pH, adsorbent dosage, and initial Cd(II) concentration were the main influencing factors affecting Cd(II) adsorption. There were significant interactions between pH and adsorbent dosage, adsorbent dosage, and initial concentration. The optimum adsorption conditions for Cd(II) with the maximum adsorption level of 89.4% were: 6.55 pH, 0.04 g adsorbent dosage, and 68.7 mg∙L-1 initial concentration. Overall, the BCB exhibited great potential as an efficient sorbent for the Cd(II) removal from aqueous solutions.