Composite samples of Na beta"-alumina with 15 vol% ZrO2 stabilized with 4.5 wt% Y2O3 were fabricated using two sintering schedules. K and Ag beta"-alumina composites were prepared from the Na beta"-alumina composite by ion exchange. The ionic conductivities of the Na, K, and Ag composites at 300-degrees-C were 1.3 x 10(-1), 59 x 10(-2) and 6.8 x 10(-3) S cm-1, respectively. K1c for the K composite was as high as 3.7 MPa m1/2.