Granulated sludge from anaerobic reactors is constituted by the microbial consortia responsible for the degradation of different substrate present in wastewaters. This study characterized anaerobic microorganisms in a granular sludge from a Uasb reactor (Upflow Anaerobic Sludge Blanket) by Most Probable Number (MPN) technique and method of cloning and sequencing the 16S rDNA gene. The main objective of this study was to quantify and to identify the microorganisms in two different culture media containing sulfate (Posgate C [6.0 sodium lactate and 3.13 g L-1 sodium sulfate] and Zinder [2.24 sodium lactate and 0.96 g L-1 sodium sulfate]). Microorganisms quantified by Postgate C and Zinder media were: 9.30x10 10 and 7.50x10 11 MPN mL-1 for general anaerobic bacteria; 4.30x10 8 and 2.10x10 8 MPN mL-1 for sulfate reducing bacteria; and 1.20x10 8 and 1.5x10 8 MPN mL-1 for methane producing archaea, respectively. Bacteria identified by 16S rDNA gene sequencing from the MPN in both culture media were related to the phyla Firmicutes and Proteobacteria. The conditions of Postgate C culture medium favored the sulfate-reducing bacteria and the Zinder culture medium favored the general anaerobic bacteria.