The richness and heterogeneity of plant and animal species, ecosystems and landscape at small area is characteristic for Slovenia. Nevertheless, according to recent data the biodiversity richness decreased due to pollution of underground and surface water, soil, air and devastation of several natural areas in Slovenia and elsewhere. In spite of the fact that the Šalek Valley is (was) placed among degradation areas, great degree of biodiversity was observed. In the Šalek Valley different ecosystems cover land: forests, shrubbery, meadows, rural and urban ecosystems, lake water, lake and river slops and marches; futhermore, water ecosystems and marches are placed within endangered ecosystems. Biodiversity richness of selected animal and plant species was monitored in the last decade by researchers of ERICo Velenje. The inventories of the following plant and animal groups were performed: (i) vertebrates (mammals, birds, amphibians, fish); (ii) invertebrates (butterflies, dragonflies, aquatic invertebrates); (iii) aquatic and terrestrial higher plants; (iv) fungi and (v) lichens, respectively. Especially intensive inventories were performed at subsiding area due to mining activities and in the vicinity of the Šalek lakes, where high biodiversity of birds, dragonflies and amphibians was determined. In addition, high biodiversity of butterflies, populating the Šalek Valley was established as well.