The investment bank boss said bitcoin is likely to collapse and said staff trading the digital currency are “stupid” and would be sacked.
The cryptocurrency “won’t end well” because “it’s a fraud,” Mr Dimon told an investor audience in New York.
His comments helped fuel a sell-off of the digital money, with bitcoin’s price sinking below the $4,000 mark on Wednesday after shedding around $1,000 since the start of September.
The JP Morgan chief said if he found a trader at the bank trading bitcoin he would “fire them in a second. For two reasons: It’s against our rules, and they’re stupid. And both are dangerous”.
Mr Dimon said bitcoin’s epic popularity is “worse than tulip bulbs,” in reference to speculators in Holland in the 17th century, who drove up prices of almost worthless bulbs.
And added that he wouldn’t even short bitcoin – bet on its downfall – because there’s no knowing how high the bubble could go before it bursts.
Mr Dimon conceded that the blockchain technology that underpins bitcoin could be useful.
But said Governments are unlikely to ever allow a currency to exist without regulated oversight.
It comes as China has launched a recent crackdown on local currency exchanges, which pressured bitcoin’s price.
The JP Morgan boss said the US could be the next country to launch a huge clampdown on bitcoin if crimes are linked to trading.
He reportedly told the New York conference: “Someone’s going to get killed and then the government’s going to come down.
“You just saw in China, governments like to control their money supply.”
However, experts said Mr Dimon’s comments could be short-sighted.
It comes after lingerie entrepreneur Michelle Mone recently said bitcoin is the currency of the future.
Naeem Aslam, chief market analyst at Think Markets UK, said: “The chief executive of JP Morgan, Jamie Dimon has said that he will not hesitate to fire his traders if they touch Bitcoin.
“The digital currency is here to stay and under a more regulated environment, its volatility would ease off.
“Moreover, this is not the first time that Jamie Dimon has spoken against the currency, the last time he had a similar go on the currency was in November 2015.
“Since then, the currency has had a remarkable run.
“Most importantly, given that the chief executive does not think that shorting this trade would yield a more favourable outcome shows that the cryptocurrency has a lot more room to run.
“The currency serves best people/nations who do not have many options on the table for themselves.”