The natural history collection is the largest in the Thuringian State Museum Heidecksburg. It contains exhibits from all areas of nature – animals, plants, minerals, rocks and fossils – as well as books, files and correspondence. In total, the collections contain about 500,000 objects.
It is thanks to the irrepressible interest in nature of Prince and later ruler Friedrich Karl of Schwarzburg-Rudolstadt that today there is a not insignificant natural history collection in Rudolstadt's Heidecksburg Palace. At a time when the thrust for research and discovery of the flourishing sciences was reflected in the numerous chambers of art and curiosities, he was able to build up a considerable cabinet of natural history himself, the founding year of which he later dated, in 1790 in the writing of his memoirs, to 1757 – a time when he was hardly able to leave his bed due to a riding accident and the subsequent convalescence period. To get through these long weeks, he was supported by his personal physician and geologist Georg Christian Fuechsel, who enriched him with his knowledge and is today regarded as one of the founders of the Cabinet of Natural History.
As early as 1729, a cabinet of rarities existed in Heidecksburg Palace, which contained many naturalia among the 341 items listed. However, a large part of it fell victim to a castle fire in 1735. Therefore, Prince Friedrich Karl's founding of his cabinet of naturalia in the Rudolstadt city palace of Ludwigsburg marked an important new beginning in princely collecting. By the end of the 18th century, it had become one of the most famous collections of naturalia in Germany.