Purpose <p>Rhizosphere is the critical soil zone surrounding a plant root where the root influences soil biological and chemical processes. Biochar, a commonly used soil ameliorant, can affect soil properties and the and metal(loid)s transformation and migration behavior. We aimed to explore the metal(loid)s transformation and migration in rhizosphere-rice system and evaluate the biochar effects.</p> Materials and methods <p>A rice pot experiments and systematically determined the impact of biochar on key rhizosphere environmental factors, rice production, and fractions and translocation of arsenic (As) and cadmium (Cd) in the rhizosphere-rice system at four rice growth stages.</p> Results and&#xa0;conclusion <p>Biochar increased pH, DOM, and SOC in the rhizosphere and raised rice biomass but decreased Eh, thus affecting the redistribution of fractions of As and Cd. The bioavailable As increased, but bioavailable Cd decreased then increased with rice growth. Biochar increased bioavailable As by 11.27–80.95% but lowered bioavailable Cd by 44.72–99.25%. The higher bioconcentration factor (BCF) of As (0.31–2.40) than Cd (0.20–0.26) suggests As is much easier to move from the rhizosphere to rice root. The higher translocation factor (TF) of Cd (0.31–0.64) than As (0.08–0.44) indicates Cd is much easier to migrate from the root to shoot and grain. Biochar reduced the As and Cd migration from rhizosphere to root and shoot, lowered Cd but raised As accumulation in rice grain. This work underscores the potential risk of As to human health through the food chain when biochar is used to remediate As- and Cd-contaminated soils.</p> Graphical Abstract <p></p>