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The fibrous envelope of the coconut tree is an agroindustrial waste product that possesses relevant properties, such as a high resistance to biological degradation, because of its phenolic compound composition. In this study, the fungitoxic activity of tannins and a tannin-copper complex from the mesocarp of Cocos nucifera Linn was conducted. An extract from the coconut mesocarp was obtained in acidic media using a 2.0 wt% solution of NaHSO 3. Bioassays were conducted on alder wood (Alnus acuminata ssp. glabrata HBK) using two types of aqueous solutions: 1) crude extract from the coconut mesocarp diluted at several concentrations (0.5, 1.0, 2.0, and 4.0 wt%); and 2) a tannin-copper complex formed in two stages by impregnation of the alder wood samples, first with the coconut mesocarp extract solutions followed by addition of a CuCl 2 solution. The fungitoxic capacity of the tannin and tannin-copper complex solutions was evaluated by means of bioassays with Trametes versicolor (L. ex. Fr.) Pilát according to ASTM D 1413-07. The bioassays showed poor fungal inhibition for the wood samples impregnated with the crude extract solutions. However, the tannin-copper complex solutions showed greater fungal inhibition. Retention values of 4.03 and 1.76 kg m-3 were obtained. These values revealed high fungal inhibition for Trametes versicolor.