The subject of the article is an experimental investigation of the actual behavior of thin-walled cold-formed C profiles used in the mezzanine systems as floor beams under the effects of static load and under the effects of fire. The aim is to determine the improved design characteristics of floor beams derived from the results of experiments, which will lead to their more economical and efficient design compared to design performed based on the rules and calculation procedures specified in the relevant European standards (Eurocodes). In total 16 static loading tests were performed on a section of the floor structure in real scale using the vacuum test method, which allows apply the uniform load. The results of static loading tests are statistically evaluated and the characteristic values of bending resistances for primary beams are derived based on the Annex D of EN 1990. Generally, the number of fire resistance tests carried out in the past on full-scale sections of load- bearing thin-walled steel structures is very limited. Therefore, standard full-scale fire resistance tests were performed on light gauge steel frame floor structures of two different configurations. First configuration includes one internal (middle) doubled primary beam and two single outer primary beams, a second configuration includes only two single outer primary beams. The fire resistance tests were performed according to EN 1365-2 „Fire resistance tests for loadbearing elements - Part 2: Floors and roofs”. Both tested configurations are classified based on the EN 13501-2 „Fire classification of construction products and building elements - Part 2: Classification using data from fire resistance tests, excluding ventilation services” and compared with the predicted fire resistance calculated according to EN 1993-1-2 „Eurocode 3: Design of steel structures - Part 1-2: General rules - Structural fire design”.The authors gratefully acknowledge to the Technology Agency of the Czech Republic – TACR (www.tacr.cz) for its support under the framework of research project FW01010206