Serpula lacrymans, the dry rot fungus, is considered the most economically important wood decay fungus in certain temperate regions of the world, namely northern Europe, Japan, and Australia. Previously, copper-based wood preservatives were commonly used for pressure treatment of wood for building construction, but some decay fungi are known to be copper tolerant. In this study, soil-block tests were undertaken to clarify the effect of copper, copper citrate, and alkaline copper quaternary-type D (ACQ-D) on the decay capabilities of S. lacrymans compared with an alternative wood preservative not containing copper. Twelve isolates of the dry rot fungus S. lacrymans and four other brown-rot species were evaluated for weight loss on wood treated with 1.2% copper citrate, 0.5% ACQ-D, and 0.5% naphthaloylhydroxylamine (NHA). Eleven out of 12 isolatcs of S. lacrymans were shown to be tolerant towards copper citrate. The ACQ-D and NHA preservatives, on the other hand, were both effective against the dry rot isolates.