Molartooth(MT)structure is an enigmatic structure which is mainly distributed in the nonstromatolitic carbonate rocks of the Precambrian. It is characterized by cracks and voids with various shapes and different sizes which are filled with homogeneous and equallysized microspar calcites. Due to its special distribution in the geologic times(from Neoarchean to Neoproterozoic)and its global distribution, there are no similar analogs in the Phanerozoic. Debates on the origin of the molartooth structure have continued until now and thus make it become the “molartooth structure enigma”. The molartooth structure developed in the micrite limestones of the Member 3 of Gaoyuzhuang Formation(from 1600 Ma to 1400 Ma)at Jixian section, Tianjin, has provided some important information for resolving the molartooth enigma. Their characters include(1)the particular configuration of the MT structures;(2)the obvious interface with rich organic matter and pyrite between the MT ribbon cracks and the host rock;  (3)the host rocks are characterized by nonstromatolitic micrite limestones with few liminites;(4)the special macroscopic fossils of algae which were simultaneously developed with the MT structures. Therefore, the MT structure can be interpreted as a type of the microbial induced primary structures formed by a complex process in a matground environment. As one of the most common sedimentary phenomena,the MT structure provides more significant information for understanding the complex Precambrian carbonate rocks.