Ceramic eutectics are naturally occurring in-situ composites and can offer superior mechanical properties. Here, ZrB2-ZrCxN1-x quasi-binary ceramic eutectic composites were produced by arc-melting a mixture of ZrB2, ZrC, and ZrN powders in an N-2 atmosphere. The arc-melted ZrB2-ZrCxN1-x composites containing 50mol% of ZrB2 (irrespective of the ZrC/ZrN ratio) showed rod-like eutectic structures, where ZrCxN1-x single-crystalline rods were dispersed in the ZrB2 single-crystalline matrices. Multiple orientation relationships between the ZrCxN1-x rods and the ZrB2 matrices were observed, and one was determined as ZrB2 {} //ZrxN1-x {111} and ZrB2 < > //ZrCxN1-x < > . The rod-like eutectic composites had higher hardness than the hypo- and hypereutectic composites and the 50ZrB(2)-40ZrC-10ZrN (mol%) eutectic composite showed the highest Vickers hardness (H-v) of 19GPa.