Within the thesis we carried out tests on fresh concrete mixtures. The main purpose of the tests was to examine the influence of chemical admixtures on rheological properties of fresh concrete. Measurement of rheological parameters was carried out with ConTec Viscometer 5 rheomether. In parallel, we also carried out slump test and flow table test on fresh mixtures and determined air content for mixtures with air-entraining agent. All concrete mixtures were composed of aggregate, water, cement and chemical admixture. As admixture, superplasticizer, air-entraining agent and stabilizer were used. We also used two different types of cement. The obtained results were analysed and comparison between shear yield stress and plastic viscosity, as well as slump and flow value were made in different times after mixing of fresh concrete.