One way to protect timber in service against basidiomycete deterioration is by means of acetylation via reaction with acetic anhydride. The reason why acetylated wood (WAc) is resistant against decay fungi is still not exactly understood. The aim of this study was to contribute to this field of science, and Postia placenta colonisation after 4, 12, 20, 28 and 36 weeks was observed at three acetylation levels of Pinus spp. sapwood. Mass loss (ML) and wood moisture content (MC) data reflected the acetylation levels. The initial equilibrium MC (EMC) proved to be a good indicator of subsequent ML. Genomic DNA quantification showed P. placenta colonisation in all samples, also in samples where no ML were detectable. The number of expressed gene transcripts was limited, but the findings supported the results of previous studies: WAc seems to have some resistance against oxidative mechanisms, which are part of the metabolism of P. placenta. This leads to a delay in decay initiation, a delay in expression of genes involved in enzymatic depolymerisation, and a slower decay rate. The magnitudes of these effects are presented for each acetylation level. The data also imply that there is no absolute decay threshold at high acetylation levels, but instead a significant delay of decay initiation and a slower decay rate.