The HfO2-Y2O3-La2O3 System was studied in the wide range of temperatures (1250 degrees -2800 degreesC) and concentrations by methods of X-ray analysis at 20 degreesC, petrography, differential thermal analysis in helium at temperatures to 2500 degreesC, thermal analysis in air using a solar furnace at temperatures to 3000 degreesC, and electron microprobe X-ray analysis. The complete phase diagram was constructed. The liquidus and solidus projections, crystallization paths for the alloys, isothermal (1250 degrees, 1600 degrees, and 1900 degreesC) and polythermal sections are presented. The structure of the boundary binary systems defines the phase equilibria in the ternary system. No ternary compounds were found. Ternary solid-solution regions were determined based on constituent oxides and intermediate phases.