It was shown in the past that different re-tanning agents were used as a repellent to enhance the antifungal properties of the hydrothermal stability of the skins of ancient book covers, including the aluminum sulphate-stabilized complex aluminum salt (Al-ЭDA). Although the skin treatment with this re-tanning agent improves the properties of the skin, the collagen structure cannot be considered very safe, i.e., it was relatively low. An additional biocidal substance, catamine AB, was used to ensure the antifungal properties of the treated leather. That is why, a new aluminum complex material has been synthesized for the skin re-tanning of the covers. As a stabilizer of aluminum sulphate, trimethylmeleme was used, for the production of which the meleme material was taken and reacted with formaldehyde. The resulting trimethylolmeleme, having three methylol groups, can form a complex salt when it interacts with aluminum sulphate. The mentioned complex material was filtered and the water part was removed from the crystals formed from the purified liquid by evaporation. The resulting complex salt is soluble, and the crystals left on the filter are insoluble. Both were tested as re-tanning agent samples on the cover leather samples. Treatment with crystals separated from the filtered liquid completely increases the welding point of the skin treated with the tannin extract of ancient leather up to 1000C and more, and up to 75-770C during re-tanning with the complex salt removed from the filter. The research of antifungal properties of the complexes has identified an expressive activity of the difficulty of dissolving complex II in comparison to the compound used earlier. High hydrothermal stability gives strength, less elasticity and other high-performance properties to the leather