It is well known that magnetic properties of electrical steel sheet deteriorate due to stress in production process of electrical apparatus. Therefore the magnetic power loss increases in comparison to design-time assumptions. Therefore, it is necessary to clarify the relationship between the stress and the magnetic property. In general, the magnetic properties of the electrical steel sheets become better by applying the tensile stress, and deteriorate by applying the compressive stress. The magnetic property under the stress has been evaluated by a scalar magnetic measurement, which means same direction for the excitation and the stress in the electrical steel sheet. We developed new measurement system, which can evaluate the vector magnetic property under the biaxial stress. In this paper, the mechanism to apply the biaxial tensile stress is examined by measuring the principal stress. In addition, the vector magnetic property under the tensile stress of x and y direction is measured with the developed system. Figure 1 shows the developed vector magnetic measurement system under biaxial tensile stress. The strain of the electrical steel sheet is measured with three-axial strain gauge. The stress components sx, sy and txy are calculated to evaluate the principal stress. The vector magnetic property is measured by using VH analyzer (IWATSU, IE131E). Figure 2 shows the vector magnetic property depending on the tensile stress of x direction. The principle stress of x direction is controlled by adding the biaxial stress in the developed system as shown Fig. 2. The trajectory of the magnetic field strength and the BH loop of x and y components under the tensile stress changed in comparison with that of the non-stress. The area of BH loop of x component becomes smaller, and that of y component becomes larger by increasing the value of the tensile stress. Figure 3 shows the magnetic property depending on the maximum principal stress of the x direction. The relative