Eutectic silicon modification is an important casting parameter on Al-Si alloys on the aspect of mechanical capability and energy absorption of the cast part. Chemical modifier element strontium has been used to obtain eutectic modification on Al-Si alloy commercially. On the other hand, high cooling rate on Al-Si alloys both refine dendrites and silicon phase which enhances mechanical characteristic. In order to find a statistical relationship between strontium amount and cooling rate, a special mold was designed in order to obtain different range of cooling rates in same cast part, then tensile test data of A356 alloy were analyzed in Minitab software. Therefore, after regression and analysis of variance tests have been proceeded, it was found that strontium amount is only dominant for lower cooling rates of < 0.9 °C.