Biochar, derived from agricultural residuals, is extensively applied to remove detrimental heavy metals from wastewater, which has dual significance for the environment protection. Herein, the sorption behavior and interaction mechanism of Eu(III) on rice straw-derived biochar was investigated by batch and spectroscopic technologies. The solution pH significantly affects the percentage of the sorption, but has little effect on the contact time. Humic substances (HA/FA) significantly enhance Eu(III) sorption with solution pH<7.0, but inhibit the sorption with solution pH>7.0. The sorption mechanism involves co-precipitation or inner-sphere surface complexation. And the chemical sorption rate is restricted by intra-particle diffusion process. Besides, the Freundlich model simulates isotherms best and the maximum sorption amount is up to 40.717 mg/kg, which correlates with the stratified structure and abundant functional groups of biochar. The thermodynamic parameters suggest that the sorption of Eu(III) on biochar is a spontaneous and endothermic process. Therefore, these results are valuable to assess the potential application values of rice straw-derived biochar for the removal of Eu(III) in water systems.