The aim of this experimental work was to design a modified test with which it will be possible to determine the fluidity of ductile cast iron. First, we planned the conceptual verification of the designed experiment, which was done by numerical simulations of the casting processes, followed by rapid mould fabrication using 3D printing. A measurement cell was placed in the mould cavity of the experimental chamber for further investigation of the cooling and solidification during casting. From the matrix of data obtained with the experiment, we defined the fluidity of the ductile iron EN-GJS-500-7. Also, we analysed the mechanical properties of the studied alloy, the microstructure, the chemical composition, and the results of the thermal analysis. In accordance with the expectations and theory from the literature, the fluidity in the experimental sample cast at a higher temperature was better than that cast at a lower temperature. Because of the faster cooling rate at the end of the channel of the experimental casting, the microstructure is fine, moreover, we obtain white solidification, ledeburite in the microstructure of the samples etched with Nital. At lower cooling rates, fewer graphite nodules appear in the microstructure, which are larger, and the portion of ferrite is greater.