Abstract The phase relations in the Ce-poor region of the ternary systems Al–Ce–(Ge, Si) were re-established at 600°C for Ce-concentrations up to 33 at.% Ce. The exact phase triangulation and structure determination for both systems were determined by EPMA and X-ray powder diffraction techniques. The homogeneity regions at 600°C were redetermined for the two phases within the section Ce(AlxSi1−x)2: CeAl1.46Si0.54(AlB2-type) and CeAl0.45–1.28Si1.55–0.72(αThSi2-type). Besides these two phases, the only compound stable at 600°C in the system Al–Ce–Si was found to be CeAlSi2with a new structure type. CeAl2Si2with the La2O2S-type, reported in earlier investigations, was shown to be metastable. Similarly, the existence of the phases reported earlier, “CeAl1.25–1.75Si2.75–2.25,” “Ce2Al3.5Si4.5,” and “Ce2Al3Si2,” was not confirmed at 500°C or 600°C. Ce3Al4Si6(Ce3Al4Si6-type) was obtained in pure form after long-term annealing of melt spun samples at 500°C. For the Al–Ce–Ge system, our investigations at 600°C confirmed the five ternary compounds known from the existing literature. Homogeneity regions and location of the ternary phases were redefined. XAS and magnetic susceptibility measurements revealed a tripositive cerium ground state,2F5/2, in all the compounds studied. CeAl1.2Si0.8, CeAlSi2, Ce3Al4Si6, and Ce2Al1.6Ge5.4are antiferromagnets withTNof 4.2, 3.7, 3.5, and 4.7 K, respectively. In turn, CeAl2Si2, CeAlGe, and Ce2Al3Ge4order ferromagnetically below 8, 5.6, and 11 K, respectively. The electrical resistivity of all these phases is characteristic of cerium intermetallics with pronounced crystal field effects.