The influence of dissolved Ce and primary inclusion particles of Ce₂O₃ (the planar mean particle diameter, d_A=1.6 to 2.1 μm) or CeS (d_A=2.4 to 2.8 μm) on solidification micro- and macrostructure was investigated in an Fe-0.20 mass%C-0.02 mass%P alloy. The primary and secondary dendrite arm spacings decreased with an increase in the content of dissolved Ce in the range between 140 and 750 mass ppm, but they tended to decrease with increasing the number of Ce₂O₃ or CeS particles up to N_A=900 mm^-2. With an increase in the number of Ce₂O₃ or CeS particles up to N_A=900 mm^-2, the area fraction of equiaxed crystals increased from 30 to 55 %, but it was found to be independent of the dissolved Ce content. The degree of undercooling reduced by increasing the particle number of Ce₂O₃ or the dissolved Ce content. The correlation between primary dendrite arm spacing and austenite grain size was discussed.