Spark plasma sintering (SPS) is one of the capable new techniques of sintering at the lower temperature for a short time. In the previous work of our group, the consolidation of SiC nanopowder synthesized by mechanical alloying was subsequently accomplished by SPS of 1700^oC for 10min under applied pressure of 40MPa. The SiC sintered compact with relative density of 98% consisted of the nano sized particle less than 100nm. This phenomenon resulted in the ordering process of stacking disordered structure formed by mechanical alloying. In this work, the effect of grain size and relative density on the mechanical properties was studied. It was possible that the density of SiC sintered compact was controlled by holding time at 1700^oC in the SPS. The SiC sintered compact had the relative density of 68% and the mean grain size of 10nm in the case of sintering for 0min of the hold time. Also the SiC sintered compact had the relative density of 98% and the mean grain size of 50nm in the case of sintering for 10min. Thus, the consolidation synchronized with grain growth. The mechanical properties of those sintered compacts were evaluated and compared with the reference samples fabricated from the commercial powder (β-SiC, 0.3mm, IBIDEN Co.) with sintering agent (B-C mixture). The Vickers hardness and bending strength of those sintered compacts increased with the increment of the density. However the mechanical properties were lower than those of reference samples in case of lower density even though the mechanical property was close to that of reference sample in case of higher density. This phenomenon was considered for the difference of bond strength between grains because those sintered compacts were fabricated without any sintering agents, while those reference samples were fabricated by accelerating the grain bonding with a sintering agent of B-C mixture.