Twenty-three-year-old Laura Cunliffe pleaded guilty to putting her four-month-old pet Mowgli in the microwave for five minutes after it apparently attacked her goldfish.
Cunliffe, from Hoyland, northern England, then removed the kitten from the appliance where the suffering animal was still alive.
The cat died about 90 minutes later after it was removed from the oven, 'Metro' reported.
The kitten had its internal organs cooked, a court heard.
"The kitten was in a distressed state when Miss Cunliffe took it out of the oven," said Brian Orsborn, prosecuting for The Royal Society for the Prevention of Cruelty to Animals (RSPCA).
The report said Cunliffe will be sentenced next month after pleading guilty to causing unnecessary suffering to an animal.