Thermal barrier coatings (TBC's) perform the important function of insulating components such as gas turbine parts that operate at elevated temperatures. The most commonly applied TBC material is yttria stabilized zirconia (3YSZ), because it has a coefficient of thermal expansion similar to that of substrate metals. In this study, 3YSZ/monazite-type LaPO4 nanocomposites were prepared by the pulse electric current sintering (PECS) method. The amount of LaPO4 added to 3YSZ was varied from 0 to 40 vol.% and thermal and mechanical properties of these nanocomposites were investigated. The XRD results of the 3YSZ/LaPO4 nanocomposites demonstrated differences in the crystalline phase of as-sintered and annealed zirconia. The phase transformation of as-sintered specimens was related to the amount of monazite-type LaPO4, but this phenomenon was not observed in annealed specimens. The density of 3YSZ/LaPO4 nanocomposites after annealing was decreased and the porosity was increased. Also, mechanical properties of 3YSZ/LaPO4 nanocomposites decreased with increasing dispersion of monazite-type LaPO4 particles. It was caused by low mechanical properties of LaPO4 and weak bonding between 3YSZ. Thermal conductivity of 3YSZ/LaPO4 nanocomposites was lower than 3YSZ. The difference of thermal conductivity between 3YSZ and 3YSZ/LaPO4 nanocomposites at high temperatures was higher than that at low temperatures.