The Southeast Asian Pupillidae, commonly known as "micro snails", are prominent and ubiquitous members of limestone ecosystems particularly on the main land countries like Vietnam Cambodia, Laos, Myanmar, Malaysia and Thailand. They exhibit various peculiar biological features, including the unique shell morphology, the highly endemism. Their taxonomy was primarily developed by Pilsbry (1916-1918a, 1935), Steenberg (1925) and Baker (1935), based on shell and some anatomical characters. Although the generic level within this micro land snail family was lack of a modern phylogenetic perspective and the use of shell morphology and molecular characters for phylogenetic utility has not been established yet. This dissertation addresses this shortcoming by conducting phylogenetic studies on the Pupillidae, focusing mainly on the subfamily Gastrocoptinae, a major subgroup of the family in Southeast Asian region. Chapter 1, 2 review the current understanding of pupillid taxonomy, classification and their unique shell morphological characters. All of materials and methods are defied in Chapter 3. Using morphological characters, Chapter 4 studies on morphometric analysis and tests phylogenetic relationships among Thai pupillid genera and, as a result, Gyliotrachela and Hypselostoma do not forming the distinctive clusters by SWA character analysis and a monophyly of each genus is not supported. However, using the shell morphology alone may contain more homoplastic and increase the risk that the similarity of the character observed is not the result of the common ancestry but rather of parallel or convergent evolution. The current taxonomy of the Pupillidae is also revised based on combined phylogenetic analyses of two different gene sequence data, mitochondrial ribosomal 16S, and nuclear ribosomal 28S (Chapter 5). Although characterized by high levels of genetic differentiation and homoplasy, the molecular dataset provided a number of novel insights into gastrocoptine evolution and systematics. Nominal conspecifics of three genera with replicate samples (Gyliotrachela, Hypselostoma and Anauchen) occupied contiguous sections of treespace, however all three were paraphyletic. Two inferred examples of reductive loss in apertural lamellae were encountered: Aulacospira smaesarnensis, was firmly nested within an otherwise exclusively Gyliotrachela tip clade; the leaf-litter-dwelling Hypselostoma panhai, exhibited striking conchological differentiation from its geographically proximate rock-dwelling sister taxon H. erawan. The results caution against the unquestioned use of apertural dentition characteristics as diagnostic generic characters, imply that ecological transitions can lead to rapid morphological change, and suggest that a comprehensive sampling of both rock and leaf-litter lineages is required to fully flesh out phylogenetic relationships among regional pupillid microsnails. This dissertation also emphasize the utility of geographically proximate gastrocoptine taxa to establishing sister relationships for locally endemic species, irrespective of apparent morphological similarity. However, not all Thai gastrocoptines have localized ranges; Krobylos maehongsonensis, has apparently experienced geographically extensive patterns of gene flow and colonization. The results of these evolutionary studies not only increase our understanding of the phylogeny of the Pupillidae, but also provide the way to conduct the precise systematic classification, an important in biological basic study.