The ruling set the stage for the return of the entire collection of thousands of posters taken by the Nazis, which are now worth at least euro4.5 million ($5.85 million).
The Berlin administrative court ruled that Hans Sachs never gave up ownership of the collection of 12,500 posters taken from his home on the orders of Nazi Propaganda Minister Joseph Goebbels.
Sachs, 71, sued in a test case for the return of two posters - a 1932 poster for "Die Blonde Venus" ("Blonde Venus") starring Marlene Dietrich, and one for Simplicissimus, a satirical German weekly magazine, showing a red bulldog. The court ruled that it was unclear whether "Die Blonde Venus" was part of his father's collection, but that there was no doubt about the Simplicissimus poster and that it must be returned to him.
The ruling means that the court has backed the claim of Peter Sachs of Sarasota on the surviving portion of his father's collection - some 4,000 posters at the German Historical Museum in Berlin, said his attorney ,Matthias Druba.
"We are definitely delighted," Druba said . "It's a shame that we didn't get the Blonde Venus, but in the end what is more important is that the general question has been answered clearly in our favor: Peter is the rightful owner of the collection and he has a claim to get them back; we couldn't want more."
The posters include advertisements for exhibitions, cabarets, movies and consumer products, as well as political propaganda - all rare, with only small original print runs.
Only a handful of the posters on display at any given time at the German Historical Museum, but officials maintain they form an integral part of its 80,000-piece collection. The museum also points out that those in storage are regularly viewed by researchers.
Collections Director Dieter Vorsteher, who represented the museum at the hearing, said he would not comment on what the loss of the collection would mean to the museum, but suggested that his side would appeal.
"It will certainly continue," he said outside the courtroom.
But the panel of three judges also rejected a countersuit from the museum in their ruling Tuesday, which might make an appeal difficult.
The museum had asked that the court rule that Peter Sachs was not the rightful owner of any of the posters in its collection, and, failing that, that he had no right to have them back.
Born in 1881, Hans Sachs was a dentist who began collecting posters while in high school. By 1905, he was Germany's leading private poster collector and later launched the art publication Das Plakat, or The Poster.
After the Nazis came to power, the collection caught the eye of Goebbels, who wanted it for a museum, and it was seized in summer 1938.
On Nov. 9, 1938, during the Kristallnacht pogrom against the Jews, known as the Night of Broken Glass, Hans Sachs was arrested and thrown in the Sachsenhausen concentration camp north of Berlin. When he was released about two weeks later, the family did not wait to see what would happen next and fled to the United States.
After the war, Hans Sachs assumed the collection had been destroyed and accepted compensation of about $50,000 (euro38,437.88) from West Germany in 1961.
He learned five years later, however, that an East Berlin museum had part of the collection. He wrote the Communist authorities about seeing the posters or even bringing an exhibit to the West to no avail. He died in 1974 without ever seeing them again.
The collection was given to the German Historical Museum in 1990, after communism fell.
Peter Sachs has said he only learned of the existence of the collection in 2005, and began fighting then for the return of the posters.
He has said he is not sure what he will do with the posters if and when they are returned, but wants them to remain accessible to the public.