Abstract: This paper refers to a 3 m thick microbialite in the PermianTriassic boundary section in Laolongdong, Chongqing. The microbialite comprises a dendroid upper part and a specked lower part. An erosional surface is found at the top of the upper part of the microbialite. Some dessication cracks occurred on the top surface of the lower part of the microbialite. Study on depositional environment of the microbialite indicates that the microbialite was emerged to the earth surface and eroded during the PermianTriassic interval, which provides new data for the sea level changes across the PermianTriassic boundary, an important geological epoch.