Fühmann returned from Soviet captivity to East Germany, where he lived for the rest of his life in Märkisch Buchholz and Berlin.

Among Fühmann's children's books are fairy tales, puppet plays, plays on the German language (Lustiges Tier-ABC, Die dampfenden Hälse der Pferde im Turm von Babel) and retellings of classical literature (Reineke Fuchs, Das Hölzerne Pferd [the Iliad and the Odyssey] and Prometheus [Die Titanenschlacht]), and he corresponded with many young readers.

The concept and the possibility of "change" (in his case, from a supporter of Nazism to a dedicated socialist) were especially important to Fühmann, and play a leading role in Zweiundzwanzig Tage oder Die Hälfte des Lebens (one of his major works, a spare diary of a trip to Hungary).

With the latter, Fühmann encouraged the publication of authors whose work had rarely appeared in East Germany (such as Georg Trakl and Sigmund Freud).

In later life he began to despair of the political conditions in East Germany (as reflected in his correspondence with Christa Wolf, Monsieur – wir finden uns wieder), and was unable to finish his long-planned magnum opus (which he called Bergwerksprojekt in his letters and notes).

His library (consisting of about 17,000 volumes, with many notes and underlinings) is part of the Historische Sammlungen of the Zentral- und Landesbibliothek Berlin.

His work still interests young artists (such as Barbara Gauger), and the Franz Fühmann Freundeskreis Märkisch Buchholz in Berlin illustrates its extent.