This study aimed to assess the natural durability of 20 Amazonian wood species preserved with chromated copper arsenate (CCA) after 30 years in ground contact in an experimental field test at National Forest of Tapajós, Pará state - Brazil. Heartwood samples with a cross-section of 5 × 5 cm and 50 cm of length were half-buried in soil and inspected every year for decay. The species were classified according to natural durability following the classification method proposed by Findlay (Findlay, W.P.K. (1985). The nature and durability of wood. In: Findlay, W.P.K. (Ed.), Preservation of timber in the tropics. Springer Science , Whitchurch, pp. 1–13). After 30 years in ground test, six species were classified as Perishable, seven as Non-durable, three as Durable and four as Very durable, namely: Trichilia lecointei , Lecythis pisonis , Pseudopiptadenia suaveolens , and Dipteryx odorata (Very durable), Protium tenuifolium , Dinizia excelsa , and Ormosia paraensis (Durable), Endopleura uchi , Goupia glabra , Pouteria egregia , Tachigali chrysophylla , Tachigali paraensis , Vatairea sericea , and Vochysia maxima (Non-durable) and Chrysophyllum lucentifolium , Couratari oblongifolia , Didymopanax morototoni , Lueheopsis duckeana , Sterculia excelsa , and Xylopia nitida (Perishable). CCA preservative treatment was effective to promote timber protection, even under harsh climatic conditions of the Amazon forest environment.