The non-metallic inclusions (NMI) have large influence on steel properties. Therefore, evaluation of inclusion size, number, composition and morphology by using modern analytical techniques are very important for control of steel production and steel quality. Three dimensional analysis method of electrolytic extraction is applied in this work. Metals are dissolved and undissolved inclusions are collected on the film filter. Scanning Electron Microscope (SEM) with Energy Dispersive Spectrometer (EDS) is applied to observe different non-metallic inclusions. Apart from electrolytic extraction, several other different methods can be used to analyse the inclusions. Each of them has their advantages and drawbacks. A part of this work compares different methods for investigation of inclusions. To modify the inclusion size, number and morphology, calcium or zirconium can be added in to the steel with certain amount according to the steel grade. This work discussed how inclusion size, number and morphology changed after the modification. In samples of Heat A, the addition of Zr leads to the appearance of ZrO2 clusters. Large size particles disappeared while the peak value for the number of inclusions per unit volume didn’t decrease. The electrolytic extraction and fractional gas analysis (FGA) results show some differences on the inclusion compositions. In samples of Heats B and C, the effect of calcium treatment is investigated. Calcium treatment modified the spinels with large content of Al2O3 into spherical CaS+CaO-MgO-Al2O3 inclusions. Large size inclusions were removed after calcium treatment.Key