Nathan Proctor, aged 25, was serving a sentence at HMP Moorland, in Doncaster, when he attacked fellow prisoner John Banks in August last year.
Proctor, who was serving an 18-month sentence for actual bodily harm, admitted grievous bodily harm after the attack and was given an extra four-year term, with another year on extended licence.
Judge Paul Watson QC, sitting at Sheffield Crown Court in April, heard how CCTV captured Proctor, of Nottingham Road, Mansfield, going into a corridor and leaning over the first-floor balcony near his cell to see who was standing below.
He then returned to his cell and emerged with a full kettle of boiling water which he then threw over the balcony and on to Banks.
He appealed today, claiming Judge Watson was wrong to find he was “dangerous offender” and imposed too long a sentence.
However, three of the country’s top judges, sitting at the Court of Appeal in London, rejected Proctor’s complaints and upheld the sentence.
Ruling on the case, Sir John Royce said the attack was a “wicked” offence, committed by a man with a “dreadful” criminal record.
He said: “The sentence was well within the broad parameters of the judge’s sentencing discretion.
“It was neither manifestly excessive nor wrong in principle.”
The court heard Proctor had singled out Mr Banks for the attack.
Sir John said: “He came out of his cell and looked down at the deck below, where the complainant was sitting.
“He returned to his cell, came out with a kettle and poured boiling water over the head and back of the complainant.
“The complainant suffered 15 per cent burns to his body surface, but fortunately when he visited a plastic surgeon, his wounds had largely healed.”
Proctor appealed on the basis that the judge had been wrong to call him “dangerous” without first ordering a report from a probation officer.
But Sir John, sitting today with Lord Justice Sir Julian Flaux and Judge David Aubrey QC, said there was plenty of evidence to suggest Proctor is a danger.
The sentence appeal was refused.