This Letter reports our detailed first-principles study on neutral and charged Ca8C12 clusters. Except a compact structure owning geometrical characters of the CaC2 bulk, all the other low-lying structures within 0.2 eV in relative total energy are hollow configurations. Most of the low-lying structures are calculated to be magnetic. The ground states are a D3d flat structure, a compact structure, and a D 3d hollow cage-like structure for Ca8C12, Ca8C12-, and Ca8C12+ clusters, respectively. The net charge on Ca ion, except the dangling one of the compact structure, is calculated to be around +1.4e.