Boriding of 34CrNiMo6 steel was performed in a solid medium consisting of Ekabor-II powders at 1123, 1173 and 1223 K for 2, 4 and 6 h. Morphological and kinetic examinations of the boride layers were carried out by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thicknesses of the boride layers ranged from 22 +/- 2.3 to 145 +/- 4.1 depending on boriding temperature and time. The hardness of boride layer was about 1857 HV0.1 after boriding for 6 h at 1223 K, while the hardness of the substrate was only around 238 HV0.1. Growth rate constants were found to be between 1.2.10(-13) - 9.8.10(-13) m(2)/s depending on temperature. The activation energy for boron diffusion was estimated as 239.4 +/- 8.6 kJ mol(-1). This value was comparable to the activation energies reported for medium carbon steels in the literature.