The invention relates to a process for the preparation of a gypsum product wherein calcium sulphate hemihydrate and/or calcium sulphate anhydrite and water are contacted so that the calcium sulphate hemihydrate and/or calcium sulphate anhydrite and the water react with each other and form a gypsum product. The reaction mixture has a dry matter content of 34-84% by weight in order to obtain a gypsum product which consists of crystals that are small, flat and of as equal size as possible. The invention also relates to a product prepared by this process. A gypsum product is formed which consists of essentially intact crystals having a size of between 0.1 and below 2.0 μm. The products are applicable e.g. as fillers or coating pigments in e.g. paper industry.