Abstract: Fermentation bacteria (FB), sulfatereducing bacteria (SRB) and anaerobic cellulosedegrading bacteria at different depths in four peat sediments were accounted and the existence of methaneproducing bacteria was investigated. The result showed that the numbers of fermentation bacteria were positively correlated with the content of organic matter, especially with those of humic acid. There is no obvious relationship between the numbers of sulfatereducing bacteria and the contents of sulfate. However, to some extent the SRB are negatively correlated with the depths of samples. The minima of both sulfate contents and SRB numbers were found at the bottoms of four sediments. Anaerobic cellulosedegrading bacteria were only detected in several samples, while methaneproducing bacteria habited in all samples even in coexistence with sulfatereducing bacteria. The corresponding geological effects of these anaerobic bacteria on peat sediments were also analyzed in this paper.