The review, which is to take in all big technology companies — which means Google, Facebook, Apple, Microsoft and Amazon — was announced by US Assistant Attorney-General Makan Delrahim on Tuesday.
Mnuchin told CNBC: "I think if you look at Amazon, although there are certain benefits to it, they’ve destroyed the retail industry across the United States so there’s no question they’ve limited competition."
And he added: "I think it’s very good that the attorney-general is going to look into this. I think it’s an important issue and I look forward to him reporting back to the president and hearing his recommendations.”
The department said in its statement: "The goal of the department’s review is to assess the competitive conditions in the online marketplace in an objective and fair-minded manner and to ensure Americans have access to free markets in which companies compete on the merits to provide services that users want.
"If violations of law are identified, the department will proceed appropriately to seek redress."
Last week, the European Commission announced a formal anti-trust investigation into Amazon to find out whether the firm's use of sensitive data from independent retailers, who use its marketplace, breached competition rules within the political bloc.
EU Competition Commissioner Margrethe Vestager said in a statement at the time: "European consumers are increasingly shopping online. E-commerce has boosted retail competition and brought more choice and better prices. We need to ensure that large online platforms don't eliminate these benefits through anti-competitive behaviour.
"I have, therefore, decided to take a very close look at Amazon's business practices and its dual role as marketplace and retailer, to assess its compliance with EU competition rules.”
Said Mnuchin: "There’s areas where [Amazon] really hurt small businesses. People had those concerns about Walmart. Walmart developed a business where small business could continue to compete with them."
He said it was not possible to define competition among all big tech outfits in the same way. "I don’t think you can talk about competition among all these companies in the same way. People talk about the FANG [Facebook, Amazon, Netflix and Google] stocks like they’re all the same. Each company is very different.”