This study examined the effect of waste particle size on stabilization performance of hazardous electric arc furnace dusts (EAFD) from steel foundries through the measurement of the temperature rise during hydration and heavy metals leaching. EAFD was characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), granulometry, and acid neutralization capacity (ANC) analysis. Portland cement was used to stabilize EAFD. Two types of paste samples, with EAFD content varying between 0% and 50% by weight, were prepared. The first type contained original EAFD, and the second contained ground EAFD with increased surface area. The increase in the temperatures of the mixes was monitored during the hydration reactions of the pastes. Ground EAFD yielded higher temperature rise rates than the original EAFD. Heavy metals leaching were determined by toxicity characteristics leaching procedure (TCLP). Pastes containing ground EAFD up to 50% yielded lower zinc and lead leaching than that of samples containing original EAFD. The results revealed that surface area of the EAFD may affect the stabilization performance and therefore care should be given to storage conditions at the foundries.