Dunlop will stop supplying tyres for the DTM at the end of this year, the series announced on Friday.
The tyre manufacturer has been the exclusive supplier to the German series since it was relaunched in 2000.
Thomas Betzler, vice chairman of series promoter ITR said: "Losing Dunlop, one of the long-term partners of the DTM fraternity, represents a true loss.
"But the fact that we part on good terms speaks for the partnership we had."
Series organisers have been evaluating bids from rival companies in the latter part of this year.
Following October's race at Hockenheim, former champions Gary Paffett and Mattias Ekstrom spent a day testing with Hankook tyres as part of this process.
Paffett told AUTOSPORT magazine after the test: "I expected more problems but the tyres were pretty good.
"It's not easy to make a tyre for these cars, but we could race with what [Hankook] have already."
Negotiations with suppliers for 2011 are still ongoing, but the series has promised to announce a new deal as soon as one is agreed.