Results from measurements of CO₂ fluxes over one and half years at Lambir Hills National Park, in Sarawak, Malaysia (4°12’N, 114°02’E), are presented. The site is located in a lowland mixed-dipterocarp forest, a major type of Bornean tropical rainforest. We defined two dryness levels using the soil water content (SWC) in the 0－50 cm soil layer. The daytime average net ecosystem exchange (NEE) was -8.5 and -5.8 µmol m^-2s^-1 under the relative wet (SWC＞125 mm) and dry (SWC≤125 mm) conditions, respectively. The response of instantaneous NEE (µmol m^-2s^-1) to variations in solar radiation (Sr; W m^-2) and VPD (kPa) was assessed. Estimated Amax was -49.1±9.0 (95% confidence Interval) µmol m^-2s^-1 when SWC≤125 mm, while when SWC＞125 mm Amax decreased to -71.7±18.4 µmol m^-2s^-1. Estimated Rd when SWC≤125 mm and SWC＞125 mm were 8.1±1.6 and 9.3±1.8 µmol m^-2s^-1, respectively.
　The NEE was estimated to be -4.83 tC ha^-1year^-1 (sink) from eddy-covariance measurements. This value, however, might have been underestimated, because of incorrect measurements of night-time NEE under stable conditions. We adopted night-time NEE inferred by the interception of light response curve between NEE and Sr. The NEE corrected by this method was estimated to be 0.75 tC ha^-1year^-1 (source).