"Today's verdict, like the one last month, defies even the most basic standards of international justice," the White House said.
The defendants were sentenced to death in a ten-minute long proceeding in a court in the southern province of Minya.
The same court also reversed 492 of 529 previous death sentences it passed in March, commuting most of them to terms of life in prison.
The White House said it was "deeply troubled" both by the mass trials and the death sentences, warning that repression of dissent would fuel instability and radicalization in Egypt.
"We urge the Egyptian government to end the use of mass trials, reverse this and previous mass sentences, and ensure that every citizen is afforded due process," it said.