Ca 0.5 Na 0.5 Cu 2.5 Mn 4.5 O 12 , CaCu 3؊x Mn 4؉x O 12 (0.54x42) were prepared at 7003C and 2600 PSI by combined sol+gel and high oxygen pressure methods. CaCu 0.5 Mn 6.5 O 12 and CaMn 7 O 12 (x5.2؍ and 3) were prepared by solid state reactions in evacuated quartz tubes at 9003C. These compounds crystallize in a bodycentered cubic variant of the perovskite structure except for CaMn 7 O 12 , which has rhombohedral symmetry. The oxidation states of Cu and Mn were investigated by X-ray absorption spectroscopy and chemical analysis. The oxidation state of Mn is near 4؉ in Ca 0.5 Na 0.5 Cu 2.5 Mn 4.5 O 12 and decreases with increasing x. Ca 0.5 Na 0.5 Cu 2.5 Mn 4.5 O 12 , CaCu 2.5 Mn 4.5 O 12 (x,)5.0؍ and CaCu 1.5 Mn 5.5 O 12 (x)5.1؍ undergo a semiconductor-to-metal transition (T SM ), CaCu 2 Mn 5 O 12 (x)0.1؍ is metallic, while the 2.04x43.0 phases are semiconducting in the range 10+400 K. All of the materials (except the x5.2؍ and 3.0) undergo a paramagnetic-to-ferromagnetic-like transition below their ordering temperatures (T C ). The CaCu 0.5 Mn 6.5 O 12 and CaMn 7 O 12 (x5.2؍ and 3.0) materials order antiferromagnetically at (T N ) 40 and 20 K, respectively. The magnetic and resistivity results are summarized in a T+x phase diagram. The ordering temperatures decrease with increasing Mn 3؉ content, hence the double exchange mechanism does not appear to govern the ferromagnetic ordering. The highest magnetoresistance reaches a maximum of ؊32% for Ca 0.5 Na 0.5 Cu 2.5 Mn 4.5 O 12 and is ؊28% for CaCu 2.5 Mn 4.5 O 12 at 4.2 K and 5 T. In general, the magnetoresistance does not occur at the semiconductor-to-metal transition and it decreases smoothly with increasing temperature or x. These materials show high sensitivity of the magnetoresistance at low applied magnetic 5elds and good temperature stability of the magnetoresistance.