Precipitation of crystalline ZrC in the surface region of dilute ZrC–NbC solid solutions (<1.0 mol % ZrC) was revealed by electron microscopy, x-ray microanalysis, laser mass spectrometry, and x-ray diffraction. The ZrC precipitation was shown to be a consequence of the diffusional decomposition of the dilute Zr1 – xNbxC solid solutions. The boundaries of the solid-miscibility gap in the ZrCy–NbCy system were calculated. The segregation energy of zirconium carbide was estimated at –33.3 kJ/mol.