In the present work, the precipitation and preferential selection of Fe-rich intermetallics in Al-Si-Cu 319 cast alloys with two Fe contents (0.3 and 0.7 wt.%) and various Mo contents (0-0.4 wt.%) were investigated. The results showed that two types of platelet β-Fe (defined as eutectic β-Fe and pre-eutectic β-Fe) and α-Fe can precipitate depending on the alloy compositions, such as the Fe and Mo contents. Generally, the addition of Mo promotes the formation of α-Fe instead of β-Fe. However, its effect on the phase competition between β-Fe and α-Fe is greatly related to the Fe content. In alloys with low Fe content (0.3%), an addition of 0.37% Mo can promote the complete precipitation of α-Fe and suppress the formation of eutectic β-Fe. However, in alloys with high Fe content (0.7%), only the pre-eutectic β-Fe amount decreases with increasing Mo addition, leaving the eutectic β-Fe almost unchanged. While both pre-eutectic β-Fe and eutectic β-Fe can be fully suppressed with a combined addition of Mn (0.24%) and Mo (0.4%). Compared with Mn, Mo exhibits a stronger effect on the promotion of α-Fe. The combined addition of Mn and Mo can achieve better modifications of both pre-eutectic and eutectic β-Fe in 319 alloys with high Fe content.