K(+)-β/β"-aluminas in the ternary system K2O-Li2O-Al2O3 were synthesized by solid state reaction using γ-alumina for alumina source. With the synthesized powder, K(+)-β/β"-aluminas tube was prepared by slip casting method using the casting molds fabricated with α-alumina powder. The casting tubes were heat treated up to 1750 ℃ and their phase formations at the high temperatures were studied in relation with type of solvents and acids which were added to slurry for the control of pH. Sintering of the casting tube was conducted from 1600 ℃ to 1750 ℃ and the influence of sintering temperature, time and solid contents in slurry on densification was also investigated. The dispersion of slurry was able to be improved by the pH control of slurry with adding acids, but those acids caused the reaction with K(+) ion dissolved in the solvent, so undesired phases could be formed consequently. Densification behavior of K(+)-beta-aluminas tubes at the high temperatures was also identified with the microstructures.