Nanocrystalline calcium bismuth titanate (CaBi4Ti4O15), which exhibits a layer structure, has been successfully synthesized by mechanical activation of constituent oxides of CaO, Bi2O3 and TiO2 in a nitrogen atmosphere at room temperature. The phase-forming calcination at elevated temperatures that is always required is skipped. CaBi4Ti4O15 derived from mechanical activation consists of nanocrystallites, which occur as aggregates of ~50 nm in sizes. It demonstrates an improved sinterability and was sintered to a density of 93.4% theoretical density at 1175oC for 2 hours. Ferroelectric properties of sintered CaBi4Ti4O15 derived from mechanical activation have been studied. A peak dielectric constant of 1049 at the Curie temperature of 774oC was measured at 1MHz for CaBi4Ti4O15 sintered at 1175oC.