Ultrathin 2D nickel(II) (Ni2+) and imidazole (Im) based zeolitic imidazolate framework Ni(Im)2 nanosheets are reported as exceptional efficient electrocatalysts for the electrocatalytic CO2 reduction reaction. Five nanometre thick nanosheets have a higher faradaic efficiency of 78.8% and a surface active site density of 1.68 × 10-7 mol cm-2, which is superior to those of thicker nanosheets and bulk Ni(Im)2.