Three commercially produced wood-cement composites were tested for decay resistance against the brown-rot fungus Gloeophyllum trabeum and the white-rot fungus Trametes versicolor. Both the wood and cement portions of a selected set of the composites were also examined microscopically after decay testing to determine the mode of fungal attack and ascertain the effects on the wood from both brown- and white-rot fungi. The composite blocks all appeared in sound condition after exposure in a soil-block test. All three types of wood-cement composites gained weight, indicating increased carbonation, a typical reaction in cement. Specimens attacked by T. versicolor had a greater weight gain than control specimens or G. trabeum-exposed samples, indicating that the white-rot fungus promoted a greater rate of carbonation than the brown-rot fungus. Microscopic observation showed that the composite samples exposed to T. versicolor were colonized only at sites where wood particles were exposed to the sample surface. These particles were often heavily colonized by fungal hyphae and contained calcium oxalate crystals. Wood particles in the interior of the samples that were completely encapsulated by cement were not attacked by the fungus. Samples exposed to G. trabeum were colonized by the fungus at the sample surfaces but extensive degradation of the wood particles, even in wood particles from the sample surface, was not observed. Only the white-rotted sample showed distinct evidence for fungal colonization with evidence of limited wood cell wall decay. Alteration of the normal pH environment of the wood is suggested as the mechanism that protects the composite from fungal degradation even under severe decay exposure conditions.