The drug had been injected into the soles of the sports shoes to look like shock-absorbing gel.
Customs officials became suspicious after finding the man's suitcase contained six pairs of trainers and almost nothing else.
Italian police said the drugs haul had a street value of more 2m euros (£1.8m/$2.2m).
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The man, who had said he flew to Rome for a short holiday, has been detained on charges of smuggling seven kilograms (15.4Ib) of narcotics into Italy.
The arrest followed a random check on passengers arriving at Rome's main airport from Sao Paulo, Brazil.
"Only an expert would have been able to tell the liquid wasn't the usual gel," Italy's financial police said.

The plan involved buying hacking tools offered by the Shadow Brokers and then protecting computers before they could be targeted by cyber-criminals.
But critics had argued that the Shadow Brokers should not benefit in this way.
One of the researchers behind the plan said the scheme was being abandoned for "legal reasons".
Some critics had warned that paying the Shadow Brokers for access to their hacking tools, even with honest intentions, could be illegal.
The Shadow Brokers previously sold access to hacking tools allegedly stolen from the US National Security Agency - but often released the vulnerabilities for free later anyway.
One of the tools was used to help spread the WannaCry malware that affected thousands of organisations worldwide, including the UK's NHS.
The hacking group currently plans to sell a new batch of security exploits, for a payment via the crypto-currency Zcash, worth about $22,000 (Â£17,000).
On Tuesday, two security researchers set up a crowd-funding campaign to buy access to the exploits, so the vulnerabilities could be fixed instead.
But the idea divided the cyber-security community.
"There's a 50-50 split on whether it is a good idea and whether it would encourage Shadow Brokers to continue their activities," said Matthew Hickey from the cyber-security firm Hacker House, who set up the crowd-funding campaign.
Others were more outspoken: "Individuals and corps funding criminals is insane," said security researcher Kevin Beaumont.
Announcing the closure of the crowd-funding campaign on 1 June, Mr Hickey said: "If you ever want to hear a lawyer shout expletives at volume down a phone, you need to call him and tell him you have created the first open source crowd-funded cyber-arms acquisition attempt.
"It transpires that should funds change hands from ours to the Shadow Brokers we would certainly be risking some form of legal complications."
Those who have donated to the campaign using Bitcoin can seek a refund, and any unclaimed funds will be donated to online rights group the Electronic Frontier Foundation.
The Shadow Brokers group has not specified what buyers will get if they pay the $22,000 bounty and has offered no guarantee that buyers will be rewarded at all.
"If you caring about loosing $20k+ Euro then not being for you... playing 'the game' is involving risks [sic]," the group said in a blog post.

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El Shehaby was roundly booed by the crowd and was called back to the stage for his failure to bow to his opponent as it contravenes judo rules.
"El Shehaby backed off after Sasson went over to him," said BBC judo commentator Mark Doran. "That is very disappointing. That is what the Olympics is not about. To his credit, Sasson just moved on."
Sasson later revealed his coaches had warned him El Shehaby might refuse to shake his hand. The Egyptian had come under pressure from some conservative voices in his homeland to withdraw from the bout.
"I knew he would do it, so it wasn't a surprise for me," Sasson said.
The International Olympic Committee said it was looking into the incident.
"The Olympic movement should be about building bridges, not erecting walls. There's absolutely no excuse for it," a spokesman said.
You can catch up on the judo here.
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A Brazilian man has been caught at Fiumicino airport in Rome trying to smuggle liquid cocaine in his trainers.
[NEXT_CONCEPT]
Security researchers have cancelled plans to buy potentially undetected software security vulnerabilities from a notorious group of hackers.
[NEXT_CONCEPT]
Egyptian Islam El Shehaby refused to shake the hand of Israeli opponent Os Sasson after losing in the men's judo at the Rio Olympics.