We attended Bridge Street, Andover, after receiving a call from a member of the public at 12.49am on Thursday 4 January.
A man in his 30s was found with head injuries and was taken to Southampton General Hospital for treatment.
A 34-year-old man from Andover was arrested on suspicion of grievous bodily harm with intent and is currently in police custody.
As part of their initial enquiries, officers closed a section of Bridge Street, but the road has since reopened.
Anyone with information should call police on 101, quoting 44180003689.
Alternatively, people can call Crimestoppers on 0800 555 111, where information can be left anonymously.