No index fossils are yet selected for defining the global Moscovian and Kasimovian stages. Conodonts are regarded as the most potential boundary marker for the two stages. Based on conodonts from South China sections, the lineage Diplognathodus benderi–D. ellesmerensis across the Bashkirian-Moscovian boundary was recognized. Diplognathodus ellesmerensis has been found worldwide and its first appearance datum (FAD) is close to the traditional Bashkirian-Moscovian boundary in the type area of the Moscovian Stage. Therefore, the evolutionary FAD of D. ellesmerensis within the lineage D. benderi–D. ellesmerensis is considered the best marker for the base of the global Moscovian Stage. As for the global Kasimovian Stage, conodonts Swadelina subexcelsa, Idiognathodus sagittalis, and I. heckeli are potential markers for its basal boundary. All these species plus I. turbatus were found in the Naqing and Shanglong sections, South China, as well as the I. swadei-I. heckeli-I. turbatus lineage has been recorded. Among these conodonts, I. heckeli has a wider geographical distribution, an unambiguous species concept, and an evolutionary lineage, and its FAD marks extinction and biodiversification events and is closer to the traditional boundary than that of I. turbatus and I. sagittalis. Thus, I. heckeli has the most potential for globally correlating the base of the Kasimovian Stage at present. However, the FAD of I. heckeli is one substage higher than the traditional Moscovian-Kasimovian boundary that can be recognized by the FAD of S. subexcelsa.