A deranged cat killer will serve hard time after admitting Wednesday to brutally beating and then burning a stray kitty outside his Bronx home.

Ernesto Bailey, 32, pleaded guilty in Bronx Supreme Court to savagely smashing the cat against the wall and running it over with a shopping cart outside his E. 182nd St. apartment on July 25, 2014.

He then wrapped the doomed and defenseless animal in a blanket, doused it in lighter fluid and set it on fire, witnesses who viewed the security video told police.

Supreme Court Judge William Mogulescu agreed to sentence Bailey to one year in jail, in exchange for the feline felon’s plea to one count of aggravated animal cruelty.

Cat-loving activists, who had nicknamed the fallen feline “Kitty Doe” and tailed Bailey at every court appearance, said one year behind bars was not nearly enough for such sickening depravity.

“I wish I could tell you that justice had been served, but I’m so demoralized,” said one advocate, Roberto Bonelli.

“I can’t believe he only got one year in jail. He set a cat on fire!”

Fellow frustrated feline lover Lisa Bandelli-Virgona also voiced her contempt.

“If he did this to a baby, he wouldn’t have even been out on bail,” she said.

State law would have allowed a judge to sentence Bailey to up to four years in prison on the animal cruelty charge, as a class E felony, though he could also have got off with probation.

As part of his plea, Bailey must register on an animal abuse database for the next five years. He also waived his right to appeal the conviction.

He was taken away in handcuffs on Wednesday to start doing time before his sentencing date of Feb. 9.