The preparation and electrical conductivity of $eta$-$Al_2O_3$ are investigated as a function of $Na_2O$ content from the-oretical composition of $eta$-$Al_2O_3$ to that of $eta$"-$Al_2O_3$. $eta$-$Al_2O_3$ $eta$"$Al_2O_3$$alpha$-Al2O3 and ${gamma}$-NaAlO2 phases appear in the calcined powder at 125$0^{circ}C$ for 2 hours. The majoity phase is $eta$-$Al_2O_3$ in sintered specimens at 155$0^{circ}C$ and 1$650^{circ}C$ for 30 mins respectively and ${gamma}$-4NaAlO_2$ phase also exists when Na2O content is over 10.39w/o ${gamma}$-4NaAlO_2$ phase does not affect the grain growth of $eta$-$Al_2O_3$ in sintering at 155$0^{circ}C$ but acts as a reactive liquid for the abnormal grain growth of $eta$-$Al_2O_3$in sintering at 1$650^{circ}C$ The electrical conduction of $eta$-$Al_2O_3$is predominated by 4Na^+$ ion. Contribution of ionic con-ductivity to total conductivity is gradually decreased with increasing temperature at given oxygen pressure and to -tal conductivity is increased by positive hole due to interstitial oxygen with increasing oxygen pressure.