The biomass o f various components of understorey plants o f a Lowland Dipterocarp Forest, between 1.5 and 5.0 m in height, was determined by harvesting 4 7 plants from a 0.01 ha plot. The total above ground biomass was equivalent to 2 .7 8 tonnes/ha, and this was made up o f 81 percent stem, 7.5 percent branch and 11.5 percent leaf. The leaf area index (L A I) o f the stratum was 0.36. Individual biomass of plant components and o f the total plant was related to their collar girth. Using these regression equations, estimates based on measurements o f collar girth in a 0.2 ha p lo t was fo u n d to be very close to that obtained by harvesting. This suggests that regression equations could be suitable for estimating biomass especially where no felling is allowed.