The dimensional stability of rubberwood (Hevea brasiliensis) modified with acetic or hexanoic anhydride was determined by the water-soak/oven-drying method. Acetylation was more effective at providing dimensional stability compared with hexanoylation below a weight percentage gain (WPG) of 10%. This was attributed to the different modification methods used with the two anhydrides. Volumetric swelling (oven-dry) due to modification was lower for acetylation compared with hexanoylation at comparable WPGs. Data were plotted in terms of anti-shrink efficiency (ASE) against a parameter ASE’. ASE’ measures the ASE in terms of the sum of volume change due to modification and water soaking. A negative ASE’ was found for hexanoylated rubberwood. This was attributed to over-swelling of the cell wall at WPGs in excess of 25%. The swelling was due to reaction of the wood with pyridine, which is known to be very effective at swelling the cell wall. Positive values of ASE’ were found for acetylated rubberwood, but there was no clear relationship between ASE’ and WPG. Although positive values of ASE’ can be attributed to cross-linking occurring within the cell wall, this cannot be assumed, since changes in wood volume, as determined from external dimensions did not correlate with changes in cell wall volume.