The Karlovac Town Museum is a regional museum and therefore collects its holdings from the broader region of the Karlovac County.
The Natural Science Department collects and catalogues geological and palaeontological objects, the flora and fauna, and also deals with ecology and the protection of nature in the region. The Department was founded in 1956 as the Department for the Flora and Fauna of the Karlovac Region. It was one of the first departments in a museum of this type in Croatia. The first exhibition was put up by Greta Jurisic with the assistance of the Zoological Museum and Ornithological Institute from Zagreb. The first exhibits were obtained from hunters and anglers from Karlovac, as well as from the Forestry School in Karlovac.
The main exhibitions presented so far were the following: Ljudevit Rossi, Davorin Trstenjak, Nature in the Karlovac Region, The Rivers of Karlovac, The Geological Past of the Karlovac Region, The Ecology of Karlovac, Pharmacy in Karlovac, The History of Parks in Karlovac, A Hundred Years of Mountaineering in Karlovac, Medicinal Herbs, Rare and Threatened Plants, The Flora and Fauna of the Plitvice Lakes, A Hunting Exhibition, A Scouts Exhibition, The Natural and Cultural Heritage in the Patriotic War and many others. Numerous rare species of flora have been discovered and registered, most notably the peat-bog plant community, the flora of a part of Zumberak and fossils in the Kordun region.