In work, the change of domain structure of CoNi microparticles caused by mechanical stress was studied. For this purpose, an array of identical square-shaped planar CoNi particles was formed on the surface of a polished glass substrate. Elastic bending of the substrate was used for creating of mechanical stress in the particles. It was shown by magnetic force microscopy, the magnetic structure of particles is possible to change from multidomain to quasi-homogeneous state by mechanical stress.