People living in the city have seen a hike to 1,285 incidents in 2017/18 - up from 1,048 the year previous.
Data from the Department for Environment, Food and Rural Affairs shows a drop in Fareham, Gosport and Havant.
Fareham had 982, down from 1,387; Gosport had 476, down from 554; Havant had 828, down from 945.
Councillor Dave Ashmore, Portsmouth City Council's cabinet member for community safety, said: '˜Fly-tipping is completely selfish and residents shouldn't have to end up paying the clean-up costs of people who carelessly dump rubbish.'
But he said the amount in weight has reduced over the years '“ and the council had 20 successful prosecutions in the past year.
He added: '˜Fortunately we have seen a reduction in the amount of waste fly-tipped, which is important because we pay for the tonnage removed.
It comes after a huge fly-tip was discovered by firefighters in Havant. The site is now being investigated by the Environment Agency.
And in September a Southsea man was fined Â£800 after admitting fly-tipping household items four times in Portsmouth.
Councillor Rob Humby, executive member for environment and transport at the county council, said: '˜I'm pleased to see that the trend of the amount of fly-tipped waste on public land in Hampshire continues to go down, and the number of successful prosecutions remains strong.
'˜We're sending out a clear message in Hampshire that fly-tipping will not be tolerated here.'
Across Hampshire, the county council received 23,000 reports of dumped waste.
Officials are repeating a warning that some operators are taking people's cash and then offloading their household waste at illegal sites.
Cllr Humby added: '˜One of the ways we're tackling this is by increasing awareness among Hampshire residents to help them understand they have a part to play.
'˜They can do this by checking any individual or company employed to take away waste from homes and business is legally registered to do so by asking to see their Waste Carriers Licence issued by the Environment Agency.
'˜Small businesses, as well as householders, can now use the Household Waste Recycling Centres in Hampshire, offering a legal, safe and convenient way to dispose of household waste.'