The solidus and liquidus temperatures of the ruthenium-uranium binary system between 50 and 100 at% ruthenium were identified. The alloys were heated in a nested crucible arrangement, with the test alloy being held in an inner tungsten-lined graphite crucible or a ceramic crucible. An eutectic isotherm of 1861 ± 20 K for URu 3 + Ru with a URu 3 melting temperature of 1938 ± 22 K was measured. The URu 3 + Ru eutectic composition was 77.5 ± 1 at% ruthenium. A U 3 Ru 4 + U 3 Ru 5 peritectic temperature of 1439 ± 16 K and a U 3 Ru 5 + URu 3 peritectic temperature of 1460 ± 20 K were measured. The solubility of ruthenium in URu 3 was approximately 0.5 ± 1 at% ruthenium, and the solubility of uranium in ruthenium was less than 0.5 ± 1 at% ruthenium. The URe 2 + Re isotherm was also verified to be 2415 ± 20 K.