The amantadine-resistance of an H5 subtype avian influenza virus(AIV) isolate was characterized.The M gene of AIV 178 isolate was obtained by RT-PCR,and sequence analysis showed that M2 protein contained S31N substitution.Animal trial revealed that the isolate was resistant to the treatment of 200 mg/L amantadine via drinking water.The results suggested that AIV 178 isolate was amantadine resistant,and the position 31 amino acid point mutation in M2 protein may confer the resistance.