The effect of CH3 and Na on diamond nucleation on hexagonal boron nitride (h-BN) was investigated theoretically by using the DFT method. The methyl and sodium species were used as substituents on zigzag edge atoms of the basal plane. Outgrowths corresponding to diamond nuclei were calculated to be energetically more stable than the corresponding growth of graphite nuclei for both types of substituents. Only small energy differences were obtained for diamond nucleation on Na and CH3 substituted h-BN edges, respectively.