Wood properties were measured for trees in lowland dipterocarp forests in West Kalimantan. In 1993 and 1994, 353 samples of 286 species were collected from trunk base of trees of approximately 5 cm in diameter, and the specific gravities (SG: oven dry weight/fresh volume) and water contents of wood including bark were measured. The SG of each species ranged from 0.21 to 0.84, and the mean Â± SD was 0.53 Â± 0.13. The wide range of SG suggests that the forest had a high diversity in wood properties. The most dominant and diversified genus in this area was Shorea, and the SG of 15 species varied from 0.21 to 0.71. The range covered SG of pioneer (six Macaranga, 0.29–0.43) and small trees in primary forests (nine Eugenia and 10 Xanthophyllum, 0.55–0.77). The SG average for tree species of secondary forests of 2–6 years old was 0.31. It was significantly smaller than that of primary forests (0.58). In a primary dipterocarp forest plot, light-wood species grew faster in diameter than heavy-wood species. Water content ranged from 0.26 to 0.76. Heavy wood had low water content. Among light-wood species, some (Shorea, Artocarpus) had low water contents and others (Ficus) had high water contents. Some riverine trees also had high water contents. These wood properties appear strongly related to the life history of trees and successional stage.