Abstract: A process for the tanning of skins applicable to lamb, goat, calf hides, or skins from other origins. The process is based in the previous modification of the collagen of the skin by covalent reaction with polyfunctional polymers with a high quantity of hydroxylic groups. The modification treatment may be carried out after bated skin or pickled skin has been previously depickled. After binding of the polymer, the reactivity of the skin substrate is modified whereby it will show a higher affinity for titanium salts, for example ammonium titanyl double sulphate, titanyl sulphate or any other soluble titanium compound.