"QE is all around us and optimism is in the air," Varoufakis said in Italy.
"At the risk to sound the party pooper ... I find it hard to understand how the broadening of the monetary base in our fragmented and fragmenting monetary union will transform itself into a substantial increase in productive investments."
"The result of this is going to be an equity run boost that will prove unsustainable."
Frankfurt unleashed its "biggest bazooka", or the €1.1 trillion (£720bn) quantitative easing programme this week. The ECB will buy around €60bn worth of public and private bonds every month up until September 2016.
It's hoped the package will ward off a bout of prolonged deflation, and boost economic growth in the ailing region.
Varoufakis also said negotiations with its international credits wouldn't be affected by the eventual roll-out of planned anti-austerity measures.
"We never said we're going to renege on any promises, we said that our promises concern a four-year parliamentary term," he said.
"They will be spaced out in an optimal way, in a way that is in tune with our bargaining stance in Europe and also with the fiscal position of the Greek state."