Magnetic properties of electrical steel sheet which is used motor cores are influenced due to mechanical stress. Therefore, it is necessary to know the magnetic properties under tensile, compressive and shear stress conditions in order to utilize the electrical steel sheet effectively. This paper presents the influence of the principal stress on vector magnetic properties of a non-oriented electrical steel sheet. The vector magnetic properties of the non-oriented electrical steel sheet are measured by changing the amplitude and angle of the principal stress to evaluate the stress effect of the motor core. From these results, it was clarified that the loci of the magnetic field strength vector and magnetic power loss depend on the amplitude and angle of the principal stress.