The present study focuses on stratigraphy of the Permo-Triassic boundary in the Haftad Gholleh in the east Arak and north of the Mahallat, which is located in central Iran. This boundary is an erosional unconformity or disconformity and as in other Iranian sequences related to the Permian contains dolomitic limestone and shale and sandstone that is disconformably located below the Triassic sequence. A detailed measured stratigraphic section has provided conodonts for the Permian–Triassic boundary (PTB) sequences at the studied area. Three conodont zones have been recognized, wich place the PTB in this section by precise biostratigraphy. The of the most upper Permian sequence belongs to the Guadalupian. The Triassic sequence consists of vermiculate limestone layers with colored shale interbeds that belong to the Early triassic therefore, the unconformity at the of Permo-Triassic boundary is a hiatus of about 10 million years.