To investigate the effects of unreacted silicon on the $alpha$/$eta$transfornation variation of morphology and mechanical strength of Sintered Reaction Bonded Silicon Nitride the mixtures of $alpha$-$Si_3N_4$ and Si powder and Reaction Bonded Silicon Nitride were heat treated. The heat-treatments were performed in Ar atmosphere in order to inhibit the nitridation of silicon. In the mixtures heat-trated at 1$700^{circ}C$ the amount of $eta$-TEX>$Si_3N_4$transformed from $alpha$-TEX>$</TEX>Si_3N_4$</TEX>was sigmoidally increased and the equiaxed $alpha$-TEX>$Si_3N_4$grains elongated with the amount of silicon and heat treating time. And large $eta$-TEX>$</TEX>Si_3N_4$</TEX>grains grown into silicon were observed. On the other hand there was no change in the heat-treatment of pure $alpha$-TEX>$Si_3N_4$</TEX>In case of the heat-treatment of RBSN the same phenomena due to the silicon appearing from the decomposition of $alpha$-Smatte and needle were observed. From the three point bending test the strength of the sintered specimens with the and without 5wt% silicon addition had 53Kg/$mm^2$ and 73Kg/$mm^2$ respectively.