Shelter Scotland's Perth Road shop was given about 60 designer dresses, along with knitwear, jackets and trousers.
The shop is selling the brand new dresses for £30 each, almost a tenth of their actual cost.
Shop manager Karen Kelbie said: "In my 20 years of managing the shop, I've never seen anything like it.
"We're all still in shock.
"What could be better than dancing the night away in a beautiful dress, knowing you've just helped a vulnerable homeless person or a family living in poor quality housing?"
The donation was made by Prego Boutique in Broughty Ferry.
Owner Liza Sinclair said: "Many of our staff and customers live very fortunate lives where we don't have to think about where we're going to sleep each night or if we're going to lose the roof over our heads altogether.
"If by doing our little bit we can make a difference to even one person, then it'll all be worth it."
Staff at a charity shop in Dundee have said they are "in shock" after receiving a donation of ball gowns and prom dresses worth more than £21,000.