Resumo. The research aimed to evaluate the efficiency of neem (Azadirachta indica) and castor oil plant (Ricinus communis) oils for the improvement of Ceiba pentandra wood resistance to xilophagous fungi in soil bed condition (field simulator). The neem and castor oil plant oils were extracted with absolute ethyl alcohol and employed in the preparation of oil solutions. Wood samples with dimensions of 1.5 x 0.5 x 15 cm (radial x tangential x longitudinal) were treated to reach a nominal retention of 10 to 16 kg of solution/m³ of wood. The samples were submitted to the action of natural micro-flora of three soils; forest, agricultural use and natural pasture soils, for 180 days. Among the tested soils, the agricultural presented greater biological activity, which damaged the samples even more. Among the tested solutions, the pure neem oil provided increased protection to samples. The prepared solutions using neem and castor oil plant oils did not protect the wood from the attack of xylophagous fungi existing in the ground.