The 20-year-old has previously been loaned out to Malaga and Vitesse joins the German club, who finished 13th in the Bundesliga last term, on another temporary deal
The Brazilian moved to Stamford Bridge from Sao Paulo in 2008 but has made only three appearances for the first team.
Piazon was loaned out to Malaga in January 2013 before spending all of last season at Vitesse where he notched 11 goals and eight assists in 29 Eredivisie appearances.
The 20-year-old was also part of Brazil’s Under-20 squad which won the Toulon Tournament in June.
Piazon will wear the No.19 shirt at the Commerzbank Arena this season.