In order to determine the behavior of the X10CrAlSi25 steel at room and elevated temperatures, a number of uniaxial tests were performed using a modern computer controlled material testing machine. Based on these tests, two types of their responses were considered. The first type of responses refers to the material properties presented in the form of engineering stress–strain diagrams. From these diagrams it is possible to derive and consequently to determine tensile strength, yield strength and a Modulus of elasticity. The second type of responses refers to creep behavior presented in the form of creep curves. Based on these curves, creep resistance of the considered material can be derived. Besides, the Charpy impact tests were performed with a Charpy impact machine to define Charpy impact energy as the basis for calculating fracture toughness. Considering tensile strength (584 MPa/20 °C) and yield strength (487 MPa/20 °C), it is visible that both of them are decreased when temperature is increased and fairly low strength levels at high temperature (tensile strength: 29 MPa/800 °C; yield strength: 26 MPa/800 °C) are measured. According to performed creep tests it is visible that this material does not belong to the materials resistant to creep.