The subject of the invention is a process for the manufacture of aqueous suspensions of copper hydroxosulphates such as brochantite or antlerite, or a mixture of both, having a high copper content by weight, by reacting an aqueous solution of copper sulphate with an aqueous suspension of copper oxide or copper hydroxide in which the mean diameter of the solid particles is less than 25 .mu.m. The invention also relates to the preparation of cupric fungicidal compositions having a copper content which may be as high as 45%, in the form of powders, granules or suspension concentrates, dispersible in water, and their use for the fungicidal treatment of crops.