This work aims to investigate the influence of Cu addition on the microstructure and mechanical properties of ductile cast iron (DCI). A step-like mold was used to study the evolved microstructures at different cooling rates. It was observed that adding Cu to DCI increased the pearlite content and refined significantly the lamellar structure. This effect was more pronounced at the thicker sections (slower cooling rates). Tensile strength improved obviously with the increase in pearlite content from 550 MPa at 27 % pearlite (0.02 wt.% Cu) to 875 MPa at 83 % pearlite (2.47 wt.% Cu). However, the elongation decreased sharply from 19 to 5 % upon increasing Cu content from 0.02 to 2.47 wt.% at 20 mm thickness. The impact toughness was affected negatively by Cu addition, where the value of toughness decreased from 65 J at 0.02 wt.% Cu to ~17 J at 2.47 wt.% Cu at 20 mm.