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Effects of Ce addition on microstructure, castability (fluidity and hot tearing sensitivity), mechanical properties and electric conductivity of commercial purity aluminum (CP-Al) were investigated through microstructure observation and performance tests. Results show that adding Ce in a CP-Al can considerably refine the grains, and has an important influence on the amount, crystallographic forms, and distribution of secondary phases. Addition of Ce also has a large impact on the fluidity and hot tearing sensitivity (HTS) of the CP-Al. With the addition of Ce from 0.1wt.% to 0.5wt.%, the fluidity of CP-Al is first increased remarkably and then decreased, and the HTS has an opposite response. The best castability of the studied alloys appears to be at 0.2wt.%-0.3wt.% Ce addition. The remarkable improvement in castability is attributed to the considerable refinement of grain structure. Ce addition can also lead to a significant rise in electric conductivity. The maximum conductivity of the as-cast CP-Al is 59.7% IACS with an addition of 0.2wt.%Ce. The T7 heat treatment can further improves the conductivity to 60.7% IACS. The Ce-induced evolution of the secondary phases is believed to be the mechanism for it.