The effects of Bi3+ addition on the sintering performance and microstructural evolution of cordierite were analyzed in this paper. Cordierite powders were prepared by sol-gel processing. As nucleating agent, the Bi3+ additive was found to promote the phase transition from µ-cordierite to α-cordierite and decrease sintering temperatures. The effect of Bi3+ on the activation of cordierite can be attributed to the nucleation of cordierite. The doping of Bi3+ increased the expansion coefficient and dielectric constant. Too much Bi3+ will inhibit the cordierite crystallization and encourage anorthite crystallization.