The purpose of this work was to study the effect of CuO as a versatile sintering agent for BaTiO3 based ceramics. The response is shown to exist in three directions. Firstly, as liquid-phase former at comparatively low temperatures. Hence, the influence of various CuO-based flux formers on the shrinkage behaviour and the microstructure development of the ceramics was investigated. Secondly, the aptitude as an internal susceptor for secondary phase initiated microwave sintering. The use of CuO as a lossy secondary phase leads to an accelerated microwave heating of the ceramics. Thirdly, the addition of CuO to BaTiO3 powders with Ba-excess results in a phase transition cubic --> hexagonal at about 1300 degreesC, which is a indication for the incorporation of Cu2+ ions into the BaTiO3 lattice at Ti sites under this conditions.