Methanogenesis and denitrification in an upflow sludge baff1ed filter (UBF) reactor were studied using glucose as a fermentative substrate. Experiments were carried out to investigate how to reduce ammonfication by changing alkalinity and COD/NO3-N ratio. Characteristics of granular sludges were examined by specifics methanogenic activity (SMA) and specific denitrification rate (SDR) tests. Microstructures of granules were examined using a scanning electron microscopy(SEM)It was found that COD was removed efficiently owing to the diverse microorganisms. In nitrate conversion, not only COD/NO3-N ratio but also influent alkalinity played important role in the ratio of denitrification and ammonification of nitrate. This reactor achieved over 95% COD and 99% nitrate removal efficiencies when influent contained 4000 mgCOD/L and 700 mgNO3-N/L at the hydraulic retention timeof 24 hours. As COD/NO3-N ratio decreased, granular methanogenic activities using acetate and butyrate as substrates increased while activities using propionate and glucose decreased. There were three types in granules according to the surface color; gray, yellowish gray, and black. Gray or yellowish gray-colored granules were composed two layers, which were composed of black inner side and gray or yellowish gray surface substances. SEM i1lustrated that both were rod-type and cocci-type microorganisms resembling Methanothrix sp. and Methanococci sp. This study showed that by control1ing the influent alkalinity and COD/NO3-N ratio, ammonification and denitrification could be manipulated.