Physical and electrical properties of ${eta}$-Al2O3 were investigated as function of Na2O content from 6.67 wt.% to 13.19 wt.%. The majority phase is ${eta}$-Al2O3 and the small amount of ${eta}$"-Al2O3 exists in the specimens sintered at 1600$^{circ}$for 30 mins. In the case of specimens with 8.54 wt.% Na2O sintered at 1600$^{circ}C$, the relative amount of ${eta}$-Al2O3 phase increases and that of ${eta}$"-Al2O3 phase decreases with increasing sintering time, and then ${eta}$"-Al2O3 phase does not exist if sintering time is over 8 hrs. As the Na2O content is increased, the 3-Point MOR and the resistivity are decreased. However, density and 3-Point MOR with increasing sintering time are decreased due to increasing the enclosed pore trapped inside of the exaggerated grains. As the sintering time is increased, the average grain size and the duplexity of microstructure are increased, and the resistivity is slightly decreased.