A bench-scale expanded granular sludge bed (EGSB) reactor was applied to the treatment of palm oil mill effluent (POME). The reactor had been operated continuously at 35 degrees C for 514 d, with organic loading rate (OLR) increased from 1.45 to 17.5 kg COD/(m3 x d). The results showed that the EGSB reactor had good performance in terms of COD removal on the one hand, high COD removal of 91% was obtained at two days' of hydraulic retention time (HRT), and the highest OLR of 17.5 kg COD/(m3 x d). On the other hand, only 46% COD in raw POME was transformed into biogas in which the methane content was about 70% (V/V). A 30-d intermittent experiment indicated that the maximum transformation potential of organic matter in raw POME into methane was 56%. Volatile fatty acid (VFA) accumulation was observed in the later operation stage, and this was settled by supplementing trace metal elements. On the whole, the system exhibited good stability in terms of acidity and alkalinity. Finally, the operational problems inherent in the laboratory scale experiment and the corresponding countermeasures were also discussed.