Abstract: Microbiolite of the Bayan Obo Group mainly occurs in Menbers H₆-H₈（Halahuogete Forma-tion）in the middle part of the group.In the middle and lower parts of Member H₆ ,we can see thetypical thrombolite horizon. Its form is almost the same as that of columnar stromatolite occurringin calcareous sandstone or sandy limestone. Member H₇ is chiefly a less developed ministroma-tolite horizon. The top 50-60 m interval in the upper part of Member H₈ is the main microbiolitehorizon ,yielding microstromatolite and thrombolite. The size of oncolite , however ,is bigger andmostly radiate in shape. Microorganism mud mounds are black mounds and variable in size occur-ring in the carbonate gorezon. Microbiolite is intimately associated with the formation ofpetroleum.