Perth mum Monique Johnson says she is disgusted and saddened after her four-year-old daughter's pet rabbit, Bob, was skinned, mutilated and left for dead.

Ms Johnson said she found the poor beloved pet on Saturday morning.

The three-week-old rabbit also had one of its ears cut off in the attack.

Bob was inside his locked cage clinging to life, his ear was on the other side. Too small for surgery, he had to be put down.

“It's absolutely psychotic,” she said.

“I just think it’s someone who has no morals whatsoever and to do this to a defenceless little bunny and just leave it there

“We'd taken it straight to the vet, the vets knew exactly what had happened straight away.”

Ms Johnson says she's now too scared to leave her precious pets outside in their enclosure.

She still faces the awful task of breaking the news to her daughter.

“She loved (him), she'd always go out there and you know she’s watched them since they were literally born.”

RSPCA WA says they're ‘disturbed’ by the report and are investigating.

WA Police are also investigating.

The maximum penalty for animal cruelty is a $50,000 fine or up to five years in prison.