January 13 1939 Otto Aumann had begun to assemble the preparation committee for establishment of the museum society with the purpose to start a museum in Krško;
September 30 1939 Museum Society for political counties of Brežice and Krško was founded in Krško;
Antiques collector Otto Aumann and academic painter Franjo Stiplovšek – leading forces of the museum society;
The start of collecting and acquiring archaeological, ethnographic and cultural-historical objects, the base of museum;
Fall 1940 setup of the first museum collection in the rooms of the deconsecrated church of Holy Spirit in Krško;
November 10 1940 museum in Krško was founded (several official titles can be found Narodni muzej v Krškem, Mestni muzej v Krškem, Mestni muzej Krško (National Museum in Krško, Municipal Museum in Krško, Municipal Museum Krško);
1941 the war has cut the initial museum work;
1945 conscious members of the former Museum Society had stopped the invader from taking the collection to Germany just before the liberation;
1945 after the liberation the museum collection was displayed in heritage protected Valvasor’s house in Krško;
First years after the war – unfavourable to the museum, lack of space and funding;
1946 Franjo Stiplovšek became the manager of the museum in Krško and the authorised person of the Commission for the estimation of damage to the cultural-historical sites in Slovenia;
1949 relocation of the museum collection from Krško to the rooms of Brežice castle;
Most of the removals and set up of the collections were done by the principal Franjo Stiplovšek and archaeologist prof. dr. Rudolf Bratanič;
Relocation of the Municipal Museum from Krško to Brežice was done in accordance with the instructions of the Ministry of Education People’s Republic Slovenia, Agency for the conservation of heritage sites in Slovenia and Local administrative people’s committee in Krško;
First collections were set up in the northern part of the castle: archaeological, cultural-historical and ethnographic;
June 26 1949 at 11 a.m. a grand opening of the Posavje Museum Brežice was taking place in Brežice castle;
1949 Franjo Stiplovšek became a principal of the Posavje Museum Brežice;
1951 set up of the national liberation fight collection and the start of scientific and research work;
1960 new exhibition rooms acquired, a historic collection dedicated to the Croatian–Slovene Peasant Revolt 1573, archaeological collection rearranged;
1962 Franjo Stiplovšek retired; Stanko Škaler (1929–1973) became a principal of the Posavje Museum Brežice.