This study focuses on evaluation of borides formed on C45 steel. Pack boronizing is carried out at a temperature range of 870 – 970 °C in durations of 4 to 8 h. Values of frequency factor (4,51·10^-4 m²·s^-1) and activation energy (199,63 kJ·mol^-1) are determined by means of Arrhenius equation. Analysis is also performed to assess the change in volume share of boride phase and the surface microhardness in the layer cross section. Results indicated that cross sectional changes of volume share of boride phase depends on boronizing temperature and duration. In addition, empirical expression showing functional relationship between them has been obtained.