"This guy is a fraud," Sanders told CNN's Jake Tapper on "State of the Union" Sunday.
"This guy ran for president of the United States saying, 'I, Donald Trump, I'm going to take on Wall Street -- these guys are getting away with murder.' Then suddenly, he appoints all these billionaires," Sanders said.
Trump selected Steve Mnuchin, a former Goldman Sachs trader and hedge fund manager, as his treasury secretary nominee; Wilbur Ross, a billionaire former banker, to lead the Commerce Department; and Gary Cohn, a top Goldman Sachs executive, to lead his National Economic Council
Sanders said Trump's Cabinet appointments and advisers directly contradict his pledge to re-institute the Glass-Steagall Act, a regulation that separated commercial and investment banks, which was repealed under Bill Clinton.
Trump signed an executive order on Friday
that sets the stage for rewriting US financial regulation in an effort to encourage more lending to American businesses.
he White House also signaled a possible shake-up of the structure of financial regulators, especially the Consumer Financial Protection Bureau. Trump wrote that regulation must "restore public accountability," a backhand reference the CFPB, which some Republicans have painted as a rogue regulator that lacks oversight.
"He is a good showman, I will give you that -- he is a good TV guy," Sanders said of Trump. "But I think he is going to sell out the middle class, the working class, of this country."
"It is hard not to laugh to see President Trump alongside these Wall Street guys," Sanders said.
CNN's Matt Egan contributed to this report.