A novel objective method of digital analysis for microscopic examination of structural elements of fused periclase was developed. Main parameters are presented, which show the difference of the newly suggested method of investigation from the usual - linear one, in which examination is done with the help of chords. For comparison there are given results of measurements (done with the help of the old and the new method) of fused periclase crystal size, produced by Magnezit Group and by other manufacturers. Testing of fused periclase containing more than 97,5%MgO and various ratio of CaO/SiO2 in periclase - carbon refractories has not found influence of this parameter on the strength of refractories in steel - teeming ladles.