The influences of different sintering aids, including Fe2O3, Fe(NO3)3·9H2O, Y2O3+Al2O3 and MgO+Al2O3+SiO2, on the nitridation of reaction bonded Si3N4/BN ceramics were conducted at 1350°C for 2h. Results indicate that the addition of sintering aids could facilitate the nitridation process resulting in higher nitridation percent due to the reactions between sintering aids and surface silica on silicon powder. When 5wt. % of Y2O3 and 2wt. % Al2O3 were added, the nitridation percent reached to 94.4%. The addition of sintering aids has obvious effect on the ratio of α-Si3N4/β-Si3N4. The increase of β-Si3N4 ratio was attributed to the direct reaction of silicon with nitrogen.