Pseudomonas putida can oxidize Mn²⁺ to produce biological manganese oxide. The formation process and the adsorption oxidation activity of biogenic manganese oxide are crucial to the control of organic/heavy metal combined pollution in water. In this paper, the interaction between acetaminophen (APAP) oxidation and Fe(III) adsorption by biological manganese oxides was studied. Results show that BioMnO_x were amorphous nanoparticles. During its aging process, its structure evolved, and the surface appearance changed from flat to dense and protruding granule. The boundary of the particles became clearer. The average particle size ranged from about 49.9 nm to 70 nm. The adsorption of Fe(III) by BioMnO_x during the formation process occurred before the oxidation of APAP, and the adsorption of Fe(III) did not affect the oxidation rate of APAP. The oxidation degradation of APAP and the oxidation rate of Mn²⁺ all fitted well with the first-order kinetic equation. The oxidative activity of BioMnO_x had certain effect on the degradation of APAP. The increased concentration of Mn²⁺ reduced the degradation time of APAP. GC-MC results show that the degradation pathway of APAP was that it was firstly oxidized to acetamide and phenolic substances such as hydroquinone and p-aminophenol, then converted into simpler substances such as oxalic acid and benzoquinone, and finally mineralized.