The 14-month old tabby and white called Pumbaa was found bleeding in a Peterborough alleyway on Saturday.
The stab wound was so deep the vet was unable to operate before Pumbaa died.
A second cat - Mischief - was shot by an air rifle in an area near to where Pumbaa was stabbed, according to the RSPCA.
It is unclear whether the two incidents are linked.
RSPCA inspector Justin Stubbs said: "These were two shocking and completely senseless attacks."
Pumbaa's owner, Kirsty Cracknell, 29, of Croyland Road, said: "I am utterly devastated about Pumbaa - he was such a soppy little mummy's boy. I just keep expecting him to jump through the window.
"What particularly breaks my heart is that I think he must have been on his way home to me, considering where he was found."

The city centre road was made pedestrians only from June to November during the redevelopment of the Westgate Shopping Centre.
Now Oxfordshire County Council has agreed to continue the policy when the centre reopens because of the predicted increase in pedestrians.
The "experimental traffic order" still has to be signed off by the government.
The closure has also been blamed for increasing pressure on other city centre roads.
When the shopping centre is finished next year there are expected to be 11 million more people using it.
Council officers have estimated the number of pedestrians using the road will increase by 145% from 4,000 per hour up to 9,800 per hour.
They have also calculated that at present, 48 buses per hour use the road.
Officers said in their report that assurances from the bus companies "do not remove our concern over pedestrian safety".
But transport boss David Nimmo Smith said he was worried it would cause increased bus traffic in other roads such as St Aldates, which he described as an "architectural gem".
The Secretary of State for Transport will now have to approve the plan before it comes into effect.

Pakistan's telecoms regulator said the ban was no longer necessary because Google, which owns YouTube, had now launched a Pakistan-specific version.
YouTube has denied claims that the authorities can filter content.
Many young Pakistanis have welcomed the lifting of the ban but some activists want details of the deal with Google.
They say there should be greater transparency of the terms agreed between Google and the government.
A Pakistan Telecommunication Authority (PTA) official confirmed to the BBC that all internet service providers had been directed to open access to YouTube.
The Pakistan Telecommunication Company Ltd posted on its Facebook page on Monday: "Welcome Back YouTube".
Pakistan's ministry of information technology said: "Google has provided an online web process through which requests for blocking access of offending material can be made by the PTA to Google directly.
"Google/YouTube will accordingly restrict access to the said offending material for users within Pakistan."
However, a YouTube spokeswoman said government requests for the removal of content would not automatically be granted.
"We have clear community guidelines, and when videos violate those rules, we remove them," she said.
"In addition, where we have launched YouTube locally and we are notified that a video is illegal in that country, we may restrict access to it after a thorough review."
She said requests by governments for content to be removed would be recorded in YouTube's Transparency Report.
Pakistan's ban on YouTube was imposed by the Supreme Court in 2012 after the US-made film Innocence of Muslims was uploaded.
The amateur-made video was condemned in the Muslim world and sparked widespread protests for its mocking portrayal of the Prophet Muhammad.
More than a dozen people died in protests in Pakistan.
Blasphemy is a crime in Pakistan and can carry the death penalty, although such a sentence has not been carried out.
Google revealed last week that it had launched local versions of YouTube for Nepal, Pakistan and Sri Lanka.
A cat's death after being stabbed with a screwdriver has sparked an RSPCA appeal for information in Cambridgeshire.
[NEXT_CONCEPT]
Councillors have voted to ban buses and taxis from Queen Street in Oxford for six months because of safety concerns.
[NEXT_CONCEPT]
Pakistan has unblocked the video sharing site, YouTube, more than three years after it was banned for posting a video deemed insulting to Islam.