Modification of eutectic Si by Sr addition has been widely investigated, however, the Sr addition depletes the AlP nucleation sites and a coarse eutectic grain is often accompanied with a high degree of porosity. In this contribution, a series of Al-10Si-0.2Mg (wt.%) based alloys with CrB2 and/or Sr additions have been investigated by thermal analysis, Thermo-Calc, optical microscopy, SEM, EPMA, EBSD, TEM and computer tomography. It was found that eutectic grains can be refined, due to the presence of CrB2 nucleation sites, instead of AlP, which is poisoned or depleted by Sr addition. Thus a refined eutectic grain and well modified eutectic Si was obtained. Furthermore, the number density of the porosity is also decreased and the distribution is located at the boundaries of eutectic grain. Improved mechanical properties, in particular elongation, were obtained. This investigation highlights the importance of refinement of eutectic grains and simultaneous modification by Sr.