"I think the Fed has gone insane", he said.
But he's also calling the drop "a correction we've been waiting for for a long time". On Thursday, the Dow Jones Industrial Average tumbled 2.1 percent - or 546 points, after having sunk 831 points on Wednesday.
Mnuchin said there is a normalization in the yield curve on bond markets.
This week's dizzying sell-offs in the financial markets have been a rude reminder the US economy is no longer relying on ultra-low interest rates to fuel growth. The Fed was plowing ahead with rate increases, while investors were evidently skeptical that growth would be persistent enough to justify higher long-term rates.
The steep drop in Asia followed Wednesday's plunge in NY, with the Dow Jones dropping almost 830 points - the biggest fall since February - after Trump's latest criticism of the Federal Reserve.
The Fed's controls the levers of the USA economy by making policy, so it makes sense that traders would be fearful when the President criticizes the agency. Nope, it's the insane ol' Fed under that chair Jerome Powell.
White House economic adviser Larry Kudlow sought to downplay Trump's comments about the Fed.
Right now, the notion that Trump is responsible for the stock market is strong, mostly because that claim has been hammered over and over-by Trump himself.
Trump said in a telephone interview on Fox News late on Wednesday night the market plunge wasn't because of his trade conflict with China: "That wasn't it".
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Similarly, every time the Fed raises rates, the cost of interest on our debt and the cost of running the US government goes up dramatically thus reducing available money to spend on infrastructure and salaries of government employees. The quick jump in yields in turn spooked equity investors amid fears that rising rates could dent corporate profits, slow economic growth and lead to a slump in stocks.
When asked if he is considering firing the chairman of the Fed, Jerome Powell, whom Trump appointed, Trump bluntly answered, "I'm not going to fire him". "But I really disagree with what the fed is doing. OK?"
But the Federal Reserve has been gradually raising its interest rates since 2015, bringing the target for its benchmark rate to a range of 2% to 2.25% last month. He also said, "No, I'm not going to fire him (Powell)".
A swoon in bond funds can be particularly unsettling for investors because they're supposed to be the safe part of anyone's portfolio, offering stability when stocks go on another of their stomach-churning runs.
Bourses in Paris and Frankfurt both lost more than 2%, while London fell 1.3%.
With inflation barely above two per cent and unemployment at the lowest in a generation, the Fed is expected to tighten once more this year, and three or four times in 2019. The US economy is strong, US earnings are strong.
The stock market is just one thing.
The Fed has less control over longer-term interest rates, which move mostly on expectations for future economic growth and inflation.
Trump said the downslide of the stock was in fact a course correction.
"We have interest rates going up at a clip that's much faster than certainly a lot of people, including myself, would have anticipated".