A novel treatment based on polyamidoamines (PAAs) for the preservation of wood against fungi and insects with a broad protection functionality, low effective concentration, and low environmental impact has been developed. PAAs were synthesized by nucleophile addition of ethanolamine (EtA) and/or 3-aminopropyltriethoxysilane (APTES) to N,N′-methylene-bisacrylamide (MBA). The molar ratios in the tested formulation were: I) MBA:EtA=1:1; II) MBA:APTES=1:1; III) MBA:EtA:APTES=1:0.5:0.5. These formulations, characterized by ESI-MS, NMR, FT-IR, were tested against: (a) the wood decay fungi ( Coniophora puteana , Coriolus versicolor, and Poria placenta ); (b) the subterranean termite Reticulitermes lucifugus, and the drywood termite Kalotermes flavicollis ; (c) the woodborer Stegobium paniceum . Tests in combination with leaching showed that formulation II and III can be utilized as fungal wood preservatives for use classes 2–3 (EN 335:2013). In addition, all PAAs formulations were equally effective in preserving wood against the subterranean termite, and formulation II was most effective against drywood termite. On the other hand, the formulation I showed good efficacy against S. paniceum .