Copper-nickel dilute alloy crystals with [111] orientation were pulled from the melt containing 0.02, 0.05, 0.1, 0.2 and 0.5 at% nickel in a stream of purified argon gas under a given condition by the Czochralski method. The distribution and density of grown-in dislocations were examined by etching the (111) faces of six transverse cross-sections. The effects of nickel addition on the dislocation formation are discussed by referring to the previous work on copper-aluminium and copper-gold dilute alloy crystals.(1) In Cu-0.02, 0.05 and 0.1 at%Ni alloy crystals, linear arrays of slip dislocations along 〈1\bar10〉 directions were formed prominently, and the mean dislocation densities in those crystals became higher than that in copper crystals.(2) In Cu-0.2 at%Ni alloy crystals, a substructure consisting of long subboundaries and dislocation clusters was introduced inhomogeneously, while slip dislocations were scarcely formed, and the dislocation densities were generally high.(3) In Cu-0.5 at%Ni alloy crystals, short subboundaries and dislocation clusters were distributed rather homogeneously, and the dislocation density became higher.(4) It was found that the effect of small additions of nickel on the formation of slip dislocations and the dislocation density was quite different from that of the addition of aluminium or gold. On the other hand, the formation of dislocation substructures in crystals containing nickel more than 0.2 at% could be attributed to trapping of inclusions at the non-planar solid-liquid interface instabilized due to constitutional supercooling, in the same way as in the crystals containing aluminium or gold by more than a certain critical concentration.