[Objectives] To prepare biomanganese oxide/biochar composite (BMO-BC) and examine its remediation performance on arsenic contamination. [Methods] The BMO-BC was prepared by cultivating Pseudomonas putida MnB1 in the presence of Mn2+ and biochar. [Results] The initial concentration of Mn2+ in the culture system had no significant effect on the growth rate and domestication cycle of Pseudomonas putida MnB1. The results of SEM-EDS and XRD analysis confirm that the adsorbent prepared in this experiment was a composite of biomanganese oxide and biochar particles. The results of arsenic pollution removal test in simulated environment showed that the in-situ formed BMO-BC composite had certain removal effect on As (III) and the presence of biochar particles and manganese dioxide in the reaction system and the manganese oxidation ability of microbial strain MnB1 affect its remediation performance to As (III). [Conclusions] When the initial concentration is in the range of 0-10.0 mg/L, the isothermal adsorption data of BMO-BC on As (III) conforms to the Langmuir model.