The phase transformation temperature from $ heta$- to $alpha$-alumina was lowered from 1214$^{circ}C$ to 114$0^{circ}C$ in DSC by treating ${gamma}$-alumina obtained by calcination of boehmite at $700^{circ}C$ for 2hrswith $alpha$-Al2O3 seeds (d50=0.36${mu}{ extrm}{m}$) and 3wt% of the alumina sol. $alpha$-Al2O3 seeds seemed to lower to the transformation temperature and the alumina sol suppressed the high temperature agglormeration. The effect was increased as the amount of the sol was increased, which was supported by TEM and particle size distribution. For an example, spherical ${gamma}$-alumina powder with d50=0.54${mu}{ extrm}{m}$ was prepared by treating the ${gamma}$-alumina with 9 wt% of the alumina sol and 3wt% of the $alpha$-Al2O3. It sintered to 99% of the theoretical density at 150$0^{circ}C$ for 2hrs. and it had relatively homogeneous microstructure with 2~3${mu}{ extrm}{m}$ sized grains.