A 71-year-old man was found "covered in blood and with numerous injuries" after a dog attack on the front lawns of Old Parliament House on Wednesday, police said.
Police were called to the scene about 10.40am after receiving reports of two men fighting, with one man beating the other with a large stick.
When they arrived, police found the victim bloody and injured and he was taken to Canberra Hospital for treatment.
The Parkes resident said he had been attacked by a man and his dog - believed to be a bull mastiff, or a similar breed - which he claimed had mauled him.
"It is alleged the offender threatened to attack him further," police said.
Police arrested a 40-year-old man at about 12.15pm and charged him with assault and allowing a dog to attack a person.
The man was notified his dog would be seized by Domestic Animal Services.
He will face court next month.