Brighton winger Solly March and Burton loanee Cauley Woodrow also got on the scoresheet in Randers as England won for the first time since Aidy Boothroyd was appointed full-time manager.
Loftus-Cheek has made just four starts for Chelsea this season but his double took his tally for the under-21s to to six in his last seven appearances.
England dominated the game from start to finish after Boothroyd made 10 changes to the side beaten in Germany last Friday.
Reading's John Swift had already gone close when Loftus-Cheek fired the visitors into the lead after 10 minutes. The chance was made by Jacob Murphy, with the Norwich midfielder breaking down the left and pulling back into the box for Loftus-Cheek to take a touch and stroke home coolly.
England doubled their lead just five minutes later after impressive captain Will Hughes stole possession and the ball was fed wide.
March cut in from the right and struck a curling left-foot shot from the edge of the area which flew in at the far post with aid of a deflection, and England continued to dictate the pace, with Woodrow forcing Jeppe Hojbjerg to save.
Read the full article on eurosport.co.uk: Loftus-Cheek scores twice as England Under-21s dominate against Denmark