The 20-year-old completed his move to the Catalan club on Monday afternoon for a fee that could rise to £135.5m should he trigger various bonuses in his contract.
Many have questioned the amount of money handed over by Barca to sign the young Frenchman, but Bartra - who spent six years in and around the club's first team before leaving for Dortmund last summer - is confident that Dembele will live up to the hype.
"He is a pure talent. It is a great signing because he is a very good player but you need to have patience with him," he told reporters. "You can't compare him with Neymar because he is only starting out in his own career but he is going to bring a lot of fun to Barcelona."
Asked about his own playing career since arriving from Barcelona in June 2016, Spain international Bartra added: "I've been in Germany for a year, in a very competitive and intense league and I'm playing for a club who always demand 100% from you.
"To also be in the national team is very important in a year like this. I want to keep growing and improving and I think I'm on the right track."
Dembele managed six goals and 12 assists for Dortmund in the Bundesliga last season.