In this study, a simple method for assessing the microstructure of ductile cast iron by using a freeware digital image processing software is described. The method is applied to three different ductile iron grades to assess their ferrite, pearlite and graphite volume fractions as well as graphite nodularity, nodule count, nodule size. All specimens were found to show good nodularity (~ 88 % by area) with different graphite average size and perimeter morphology. The amount of graphite was also found to be similar (11±2 % by area) in all specimens. On the other hand, ferrite percentages were found as 85.8, 57.1, and 52.5 % respectively for ASTM A536 grades 60-40-18, 65-45-12, and 80-55-06. It was also found that among these three grades, the higher the pearlite content, the higher the hardness. The agreement with the standards confirms that quantitative metallography through image processing is a powerful tool in order to estimate the mechanical properties of cast irons.