Arsanilic acid (ASA), copper ion (Cu ) and phosphate (PO ) are widely used as feed additives for pigs. Most of these three supplemented feed additives were excreted in feces and urine. Anaerobic digestion is often used for the management of pig manure. However, the interaction of ASA with Cu or PO on anaerobic digestion is still not clear. In this study, the influence of ASA, Cu , PO and their interaction on anaerobic digestion of pig manure and the possible mechanisms were investigated. The initial concentrations of ASA, Cu and PO were 0.46 mM, 2 mM and 2 mM in the anaerobic digester, respectively. The methanogenesis was severely inhibited in the assays with only ASA addition, only Cu addition and ASA+ PO addition with the inhibition index of 97.8%, 46.6% and 82.6%, respectively, but the methanogenesis inhibition in the assay with ASA+ Cu addition was mitigated with the inhibition index of 39.4%. PO had no obvious impacts on the degradation of ASA. However, Cu addition inhibited the degradation of ASA, mitigating the methanogenesis inhibition. The existence of ASA would inhibit methanogenesis and generate more toxic inorganic arsenic compounds during anaerobic digestion, implying the limitation of anaerobic digestion for ASA- contaminated animal manure. However, the co-existence of ASA and Cu could mitigate the inhibition. These results could provide useful information for the management of anaerobic digestion of pig manure containing ASA with Cu .