A member of the public found the animal in a case next to communal bins on Farquhar Road, Aberdeen.
The female German Shepherd was in very poor condition and very underweight, the Scottish SPCA said.
The animal welfare charity has launched an investigation and is appealing for information.
Scottish SPCA chief inspector John Carle said: "This poor dog appeared to be very underweight and it looks as though someone has just dumped her like rubbish, as she was found next to communal bins.
"She was a female German Shepherd around 11 years old and was wearing a collar with no identification tag.
"A vet report concluded that she was in very poor body condition, although we have been unable to establish the cause of death.
"Our inquiries are ongoing and we are keen to speak to anyone who recognises the description of the dog and can tell us who owned her, or anyone who spotted someone carrying a suitcase in the area."
The Scottish SPCA was told about the discovery on April 30.