Jacob Rees-Mogg said he finds it "quite extraordinary" that Jeremy Hunt opposes tax cuts for high earners.
In a head-to-head debate last night, Mr Hunt attacked leadership rival Boris Johnson over his pledge to raise the high-rate income tax threshold from £50,000 to £80,000.
He accused Mr Johnson - who is the leadership race frontrunner - of sending out a signal that the Conservatives were a "party of the rich".
But Mr Rees-Mogg - who is backing Mr Johnson - said he couldn't understand why a Conservative was not in favour of lower taxation.
"It completely ignores the fact that 2.5 million have been dragged into the higher rate of tax since 1990, who are not oligarchs, they're not particularly rich," he told talkRADIO's Julia Hartley-Brewer.
"They are people who are only moderately well off. You're talking about police inspectors, headteachers of primary schools. You're not talking about the super rich."
He continued: "You help the least well off by growing the economy, getting more revenue for the government, and then you have the ability to fund public services."
When asked by Hartley-Brewer why Mr Johnson was not prioritising lower earners with his tax pledge, Mr Rees-Mogg replied: "How do you help the people at the bottom of the pile most? By growing the economy."
"The Conservative Party believes the government should only take the money it needs from taxpayers. Taxpayers have a right to keep as much of their own money as possible," he added.