A study on chemical modification of mbberwood (Hevea brasiliensis Muell. Arg) with acetic or hexanoic anhydride was carried out. Dimensional stability (DS) testing was carried out based on water-saturation (WS) and oven-drying (OD) cycles. DS property of acylated mbberwood was improved where a reduction in volumetric swelling coefficient (S) and increment in anti shrink efficiency (ASE) were observed. An ultimate ASE value for acetylated and hexanoylated rubberwood of 80 % and 95 % was recorded. It was found that the DS afforded to acylated rubberwood was due to bulking rather than hydroxyl (OH) substitution. Analysis of volumetric change of acylated rubberwood _showed that there is no differences between helium pyc!10meter and microcaliper data,' suggesting that the lumen volume does not change substantially, therefore microcalipers can be used to measure volume increase of the cell wall in this case. It was found that the measured molar volume (MV) is slightly lower than theoretically predicted for acylated rubberwood. Therefore based on all analyses, it was concluded that bulking is equal to the amount of bonded adducts added. Biological decay of modified rubberwood was also studied. Mass loss (ML) was reduced with increasing WPG after exposure to Coniophora puteana, Phanerochaefe chrysosporiurn and Trarnetes versicolor. The threshold (WPG) of acetylated rubberwood exposed to these fungi was 10 %, 6 % and 8 % respectively, whereas the threshold of hexanoylated rubberwood exposed to these fungi was 26 %, 17 % and 35 % respectively. Hydroxyl (OH) groups substitution is proposed as the decay protection mechanism of acylated rubberwood exposed to C. puteana, P. chrysosporiurn and T. versicolor rather than bulking. Hydroxyl (OH) groups substitution is thought to chemically and sterically supress the lower molecular weight diffusible agent (LMWDAs) activity. It is suggested that data on EMC, fibre saturation point (FSP) and size of voids of each modified sample is required to study the decay protection mechanisms of acylated rubberwood. Decay ML is reduced as the ASE increases suggesting that bulking has reduced the fungal activity to some extent.