A study has been made of the grinding of composite cements produced from clinker and two additional interground additives such as granulated blast-furnace slag, fly ash, trass and limestone, The grindabilities of composite cements depend on the grindability of the individual components, In case of intergrinding the interaction of the individual components plays a positive role. It has been stated that the particle size distribution of the ground products consisting of three components well follow the RRSB-distribution thus enabling this type of distribution to describe them. The particle size distribution of the ＇＇composite ground products＇＇ depends on their grindability and nature: the easier grindable interground additives promote the formation of wider particle size distribution. For approximately identical composition the fly ash and limestone have more widen particle size distribution than e.g. the trass. The presence of easier grindable components leads to wider particle size distribution and generally to lower mixing water demand. The water demand of composite cements with pozzolanic components is higher, especially in the presence of trass. In order to achieve standard strength the composite cements should be ground finer than the non-blended ones.