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Activated carbon from Acacia mangium wood was prepared by chemical activation using H3PO4 under optimum conditions (OAMW-AC). In this study, a rotatable central composite design of response surface methodology was used to optimize the adsorption capacity of OAMW-AC against caffeine molecules. The maximum removal capacity of the OAMW-AC was found to be 29.2 mg/g under optimized conditions. The experimental results established optimized conditions for maximum caffeine removal were; 61 min of contact time, 3.0 g/L of adsorbent dosage, 100 mg/L of initial caffeine concentration, and 7.60 solution pH. The surface morphology, surface elemental composition, and surface functional group changes on the OAMW-AC were monitored by field emission scanning electron microscopy images, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy, respectively. The characterization data showed OAMW-AC had a Brunauer-Emmet-Teller (BET) surface area of 1767 m2/g with dominated mesopore area (94.8 %). The pH at the point of zero charges (pHzpc) was 2.25, and the negative value of proton binding capacity (Q = − 0.23 mmol/g) showing proton dissociation from the carbon surface at pH above pHzpc. A desorption study of the caffeine through 95 % ethanol solution was also carried out. It was observed that 37.2 % of the adsorbed caffeine could be reclaimed from activated carbon.