The objective of this work is development of a high efficiency biomass adsorbent on the base of a carboxylate-rich wheat straw for separation and recovery of Ce3+ from wastewater. Surface-initiated atom-transfer radical polymerization (SI-ATRP) was adopted to prepare the material with uniform and well-defined polymethacrylic acid (PMAA) brushes grafted on wheat straw (WS) surface under mild conditions. The adsorption performance of the modified wheat straw (WS-g-PMAA) was then systematically investigated. Due to the presence of abundant and highly accessible carboxyl groups in the PMAA brushes, WS-g-PMAA demonstrated exceptional adsorption capacity of 298.56mg·g−1 for Ce3+, significantly higher than most reported bio-adsorbents. Moreover, the adsorption equilibrium could be achieved quickly (<180min). Full kinetic and thermodynamic investigations as well as isotherm analysis were also undertaken. In addition, the regeneration experiment indicated that the adsorbent has the advantages of good reutilization character and a stable desorption efficiency. The study suggests that the carboxylate-rich wheat straw composite is a promising adsorbent for recovery of REE ions from aqueous solution.