To full utilization of crushed straw in civil engineering industry is necessary to know its technical parameters. During previous projects on VŠB – TUO, Faculty of Civil Engineering have found parameters like settlement, thermal conductivity or airborne sound insulation. The research on these parameters have had favorable results, therefore the research is going on and other characteristics of crushed straw are finding out. These days the research team deals with determination of important fire characteristics of crushed straw. Fire characteristics play substantial character by building materials and their design in buildings. Nature materials are generally regarded as flammable. If some material is pressed, the same rule as in the phonebook – if you ignite one sheet of paper, it burns. But if you try to ignite the whole phonebook, it will be not so easy. This article is reported the first step of research on the reaction to fire. This is the preliminary classification of crushed straw into reaction to fire. The test was made according to methods which are described below. There are some changes in methods due to different structures of crushed straw.