Stainless-steel slag is considered a hazardous waste because it contains significant levels of hexavalent chromium. In the present study, the effect of boron oxide addition on the chromium distribution in Cr-bearing phase and emission of hexavalent chromium has been investigated using 2, 4, and 8 wt % addition at three different temperatures. Thermogravimetric differential scanning calorimetry (TG-DSC) and the binary phase diagram of CaO-Cr2O3 were used to find out the temperature range for the formation of hexavalent chromium. Besides, the treated samples were characterized using X-ray diffraction (XRD), scanning electron microscope-energy dispersive spectrometer (SEM-EDS), NII-1 ImageJ software and thermodynamic package FactSage 6.4, respectively. Additionally, emission of hexavalent chromium in the treated samples was detected used modified HJ 687-2014 and GB/T 15555.4-1995 after three high-temperature treatments. Finally, the research showed that chromium was enriched in the stable spinel phase and a lower addition of boron oxide content makes a lower emission of hexavalent chromium.