Compositionally triphasic boehmite-silica-zirconia composite gels were prepared by a multiphasic sol-gel route. Phase-formation characteristics and densification behavior of the gel compacts were examined with and without $alpha$-Al2O3 seeding. In the unseeded triphasic gels, both $alpha$-Al2O3 and mullite crystallize simultaneously at 130$0^{circ}C$. On the other hand, the $alpha$-Al2O3 seeding selectively induces the formation of corundum phase ($alpha$-Al2O3) at a significantly lower temperature (~110$0^{circ}C$) and facilitates an epitaxial growth of $alpha$-Al2O3 between 1100~130$0^{circ}C$. The densification of alumina-mullite-zirconia composite (derived from the triphasic gels) was also enhanced by the $alpha$-Al2O3 seeding, and this was attributed to the delayed crystallization of mullite in the $alpha$-Al2O3 seeded gel.