The genus Micryletta is widely distributed in South China and Southeast Asia. Although significant progress has been made in the diversity and taxonomy of this genus over the past few years, the distribution range and taxonomy of some species still remain controversial, especially in M. inornata sensu lato. Consequently, limitations at national borders have resulted in a lack of comparative research on species from different countries. To resolve the classification dispute, assess species diversity, and determine the distribution range of Micryletta, a series of specimens were collected from the Yunnan Province of China and Thailand during herpetological surveys from 2009 to 2020. Subsequent analyses based on morphological and molecular data revealed a distinct and previously unknown lineage from western Thailand, which we formally describe as a new species. Furthermore, our study confirms that M. 'inornata', previously known from Mengla, Yunnan, was actually M. menglienica, and further extends its distribution range to Thailand and Laos. In addition, our findings extend the latitudinal distribution of M. inornata and M. subaraji northward into southern Thailand. Notably, this study brings the total number of known species in the genus Micryletta from 13 to 14, with the count rising from three to six species in Thailand and from one to three in Laos. Our study further confirms that species diversity within the genus Micryletta is underestimated and emphasizes the important role that international collaborations play in taxonomy. Intensifying field surveys in other regions (e.g., Myanmar, Vietnam, and Guangxi of China) will be extremely necessary in the future to clarify any taxonomic questions and reevaluate the distribution range of these species.