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The objectives of this research were to evaluate the natural resistance of nine woods from the Brazilian semi-arid region to fungi under field simulator condition and to correlate the wood natural resistance with the wood density and the content of extractives soluble in hot water. The studied woods were Prosopis juliflora, Anadenanthera colubrina var. cebil, Myracrodruon urundeuva, Schinopsis brasiliensis, Senna siamea, Tabebuia aurea, Amburana cearensis, Tabebuia impetiginosa and Aspidosperma pyrifolium. Test samples measuring 0.5 x 1.5 x 15.0 cm, with the largest measure taken on fiber direction, were obtained from four positions on pith to bark direction in the stem. The samples were submitted to the action of natural microflora of three soils; forest, agricultural use and gramineous plant soils, for 180 days. Wood resistance to decay was affected by the bark-heart wood position. Just for M. urundeuva, the wood resistance was associated to wood density and extractives content soluble in hot water. The resistance of P. juliflora, A. columbrina, T. aurea, and T. impetiginosa woods was not associated to density nor the extractive content. The sp-wood was the most attacked position for all soils. Among the tested soils, the one for agricultural use presented the lowest biological activity, presenting lower deterioration for the tested woods.