The nonuniform shrinkage has been investigaed in pressureless sintering of $alpha$-SiC, where born carbide and phenolic resin as a carbon source are used as densification aids. Compacted specimens, prepared from the granulated powder, were sintered at 215$0^{circ}C$ for 30min in Ar atmosphere. Using the fresh and unseasoned graphite crucible, the upwarped specimens were obtained, while specimens were uniformly shrunk in the seasoned crucible. This effect is mainly due to the nonuniform distributjion of boron carbide during heatig, which originates in the reaction of boron carbide with CO gas, providing from the result of SiO2 reduction with carbon during heating.