The alarm about an injured person at an address in Luleå came at 1pm on Friday afternoon.
A 25-year-old man was arrested on the spot on suspicion of having injured another man in his 60s with a knife. The men must have a relationship with each other.
The injured man is said not to have suffered life-threatening injuries.
The site has been cordoned off and technical investigations are to be carried out. The arrested man must be interrogated and prosecutors must decide whether he should be arrested.
The case is initially being investigated as attempted murder.