Gurlitt died in May, months after German authorities said they had seized more than 1,000 works at his apartment, and designated Switzerland's Kunstmuseum Bern as his heir. In November, shortly before the museum accepted the bequest, Gurlitt's cousin Uta Werner challenged his will.
Gurlitt had reached a deal with the German government, binding on any heirs, to check whether some works were looted from Jewish owners by the Nazis.
The Munich court handling Gurlitt's will said Thursday it rejected Werner's challenge and found his will valid. Werner's spokesman, Thomas Pfaff, said her lawyers will examine the decision and she will then decide whether to appeal.