The 43-year-old victim was with another man in Waverley Road, Southsea, when they saw a group of youths at a phone box at the junction with Lowcay Road.
One of the children then hit the victim with the bottle.
It happened between 2.15am and 2.45am today.
The children ran towards Wimbledon Park Road.
Detective Constable Pete Bambury, from Portsmouth CID, said: ‘This was a seemingly unprovoked attack on two men walking home after a night out.’
The victim is recovering. Call police on 101 .