The effect of eutectic Si particles distributions on ductility in JIS AC4CH aluminum casting alloy (referred to as AC4CH alloy) was investigated through experimental approaches. AC4CH alloys were subject to ECAP processing at the 2nd, 4th, 6th, and 8th - passes to prepare samples with various distributions of eutectic Si particles. First, a method for the quantitative evaluation of the distribution of the eutectic Si particles using an area grid was examined. The eutectic Si particle distributions were quantified for each plane in the test pieces for unprocessed and ECAP processed samples. These quantitative values corresponded with the eutectic Si particle distributions visually observed on the microstructural images. The relationship between the quantified values of eutectic Si particle distributions and the elongations obtained by the tensile test were investigated. The uniform, local, and fracture elongations determined by the tensile test were found to increase as the number of ECAP passes increased. After the 8th - pass ECAP processing, elongation increased by 49%, 64%, and 54%, respectively in each of these types, compared to the unprocessed samples. Correlation was found between the mean quantified values of eutectic Si particle distribution and elongations. The experiments confirmed that the homogenization of the three-dimensional distribution of eutectic Si particles leads to increasing elongation.