The paleontological study of the mammalian fossils of Tertiary fossiliferous localities from Thailand, has led to the description of numerous new taxa, the modification of several extant paleobiogeographical patterns and identification of accurate dates for the Tertiary continental basins. The Krabi Basin yielded 27 distinct mammal species, most of them representing new forms, and an Upper Eocene age is now well established for this southern locality. The use of the Krabi assemblage as a reference fauna also led to the reassessment of the ages of several other Asian localities and suggests that the Thai assemblage lived in a forest under a tropical climate. All localities from northern Thailand occur in a time span ranging from 16 to 14 Ma. The use of the cenogram method, allowed the paleoenvironment of the Neogene Thai localities to be compared with contemporaneous faunal communities from the Pakistan Siwaliks and China. The middle Miocene environment in South Asia seems to have been quite open, with a likely monsoonal climate. Finally, the ages of different fossiliferous localities from Thailand are correlated with the geodynamic events following the India-Asia collision.