In this work, an attempt at determination of mechanical properties by means of a method based on magnetic Barkhausen emission measurements was proposed. The specimens made of P91 steel were subjected to creep or plastic flow which were interrupted after a range of selected time periods in order to achieve specimens with an increasing level of strain. Subsequently, measurements of magnetic Barkhausen emission were carried out; and then static tensile tests were performed in order to check variations of basic mechanical parameters. It is shown that evident relationships between the yield point/ultimate tensile strength and some parameters of the Barkhausen emission exist.