Tyres and mattresses were among the items dumped in the reserves
Fridges, burned-out vehicles and asbestos were among the items dumped in Scottish Wildlife Trust nature reserves last year.
The charity said it spends about £15,000 per year cleaning up after illegal fly-tippers and litterers.
It said it had seen "significant" fly-tipping in rural Aberdeenshire, the Scottish Borders and East Lothian.
The trust said urban sites in the central belt, including Dundee and Irvine, were the worst affected.
Other items dumped on the reserves included tyres, carpets, mattresses and building and plumbing waste.
The charity has to hire contractors to remove larger items
The trust said the total cost included staff time and hiring contractors to remove large items and hazardous substances.
Further costs were incurred by putting preventative measures in place, including installing height barriers to the trust's car parks.
Head of reserves Alan Anderson said: "Fly-tipping is illegal and it poses a danger to both people and wildlife.
"It's sad that some thoughtless individuals are dumping their waste on our reserves, forcing us as a charity to use our supporters' money to clear up after them.
"Unfortunately the actions of a few people mean that many of our staff and volunteers have to spend a great deal of time clearing up rubbish when they could be working on more important projects such as creating and restoring wildlife habitats."
