It is shown that in the system ZrC-ZrB2 there is virtually no intersolubility of the components up to 2100°C, and it is only at a temperature of 2650°C that some dissolution of ZrB2 (<2 wt.%) is observed. Using data yielded by x-ray diffraction and metallographic examinations and measurements of the initial melting temperatures of ZrC-ZrB2 alloys and of the microhardness of their structural components, a constitution diagram has been constructed for the system under investigation. The diagram is of the eutectic type, with Te=2660±40°C and a eutectic composition of 57 ZrB2 and 43 mole% ZrC.