The 43-year-old woman was placed on a 12-month good behaviour bond and banned from owning animals.
The surviving cat, since named Trooper, has recovered and found a new home.
RSPCA South Australia chief inspector Andrea Lewis said it was a "heartbreaking" case for staff.
"They see some pretty awful things," she told the BBC. "But this is something that will stay with them for a long time."
Video footage recorded by the RSPCA shows the house littered with mess, including animal faeces.
"Is that a dead cat that`s been eaten by the other cats?" an inspector asks.
"Yeah, there`s a couple," another replies.
The owner was convicted of animal cruelty in the Port Adelaide Magistrates Court.
Ms Lewis urged people to contact family, neighbours or an animal shelter if they were no longer able to care for their pets.
"People should just never walk away and leave their animals," Ms Lewis said. "Everyone has a legal obligation to look after animals in their care."
Trooper has been adopted by a family in Adelaide.
"He has made a great recovery," Ms Lewis said. "He`s a much loved member of their family."
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