The crystal structure of blue, orthorhombic (space groupP212121) modification ofbis-(L-N,N-dimethylisoleucinato)aquacopper(ii) was solved by X-ray diffraction and refined toR= 0.047. The coordination geometry around the copper atom is described by tetrahedrally distorted pyramid, with N-Cu-O angles varying from 83.4° to 97.6°. The variation in distance of Cu-O bonds (1.900 and 1.949 Å) is considerably greater than the same variation of Cu-N bonds (2.014 and 2.019 Å). The copper-oxygen distance (from ligated water) is 2.448 Å which is significantly longer than the Cu-O bonds in chelate rings.