Southsea Castle will receive £200,000 and Square Tower - one of the oldest parts of the fortifications of Portsmouth - will benefit from £250,000.
The Round Tower and Cumberland House Natural History Museum will also get a combined upkeep fund of £150,000.
The funding is part of the council's capital budget.
Linda Symes, Portsmouth City Council's cabinet member for culture, leisure & sport, said: "Everyone in the city enjoys these fantastic buildings and places but people don't often realise the work that goes into making sure they look their best and are safe to use.
"This work will ensure we can all continue to enjoy these sites for years to come."
Historic sites in Portsmouth will receive £1m for essential maintenance work.