Notranjska Regional Park is an area in the heart of south Slovenia, with a lot of unique natural sites and sites of cultural value, as well as a big diversity of flora and fauna. This diversity can be well seen through the number of butterflies, which are represented with 126 species, 90 of them were found during this research, among which the most common are Aporia crataegi, Gonepteryx rhamni, Leptidea sinapis, Coenonympha arcania, Lopinga achine, Maniola jurtina, Melitaea athalia ter Polygonia c-album. These insects are also a very good indicator of the current state of environment, mostly because of their short generation periods and complex habitat requirements. In this work we present the results of a three years long sampling (2011-2013) of the butterfly fauna on 18 different locations, scattered throughout the regional park. The next pages contain detailed information about Notranjska Regional Park focusing on butterfly diversity in the whole area as well as on the individual locations, with the emphasis on the species included on the red list of endangered species of Slovenia. We found 16 species included on this list of endangered species and 2 on the Supplement II of habitat directive. We also suggest a few measures on how to maintain the connection between people and nature, which is really strong in this area, and is one of the main reasons for preserved and diverse environment that characterizes this part of Slovenia.