Executive officer Sophie McSkimming said the cat was ''obviously left there to die''.
''It was a disgraceful act.''
The cat was discovered by Department of Conservation ranger Arnie Elbers, who said yesterday he saw a pillowcase on the roof of Conservation House, in Stuart St, on Tuesday afternoon.
When he returned to the department's ''smoko room'' on the roof on Wednesday, the pillowcase, which was securely tied, was still there.
''I gave it a bit of a touch with my foot, and it rolled all by itself, and I gave it another nudge and it growled.''
He left the growling animal in the urine-soaked pillowcase and took it to the Otago SPCA.
''I never opened it because I wasn't sure what was in there - if it was a diseased or wild thing.''
He suspected somebody had climbed the fire escape at the rear of the building and dumped the cat on the roof on Monday night or Tuesday morning.
SPCA Otago animal manager Grace Hepburn said when the pillowcase was opened a hungry 2-year-old cat emerged.
A vet check revealed it was healthy and had ''excellent'' body condition, she said.
''It had been well looked after.''
The cat was not microchipped, but was wearing a red flea collar and was ''smoochy'' and purring.
''She has lost no trust in humans,'' Miss Hepburn said.
She was ''disgusted'' by the act.
The SPCA was trying to identify the owner and the person who dumped the cat.
CCTV footage from the area was being collected and tenants in nearby buildings interviewed.
Whoever dumped the cat could be imprisoned for up to a year and fined up to $50,000, she said.
Anybody with information about the cat or who witnessed suspicious behaviour around Conservation House was asked to contact Otago SPCA.
