Abstract: A study on external characteristics of 749 live Hill Mynahs throughout Thailand classified morphological variants into five groups including two known subspecies and three new groups: northern, modified northern, intermediate, modified southern and southern. Zoogeography of these variations was studied by mapping the locations where each group inhabited related with body mass in order to understand the occurrence of three new Hill Mynah groups. The results showed that there were only northern group inhabited between 16o and 20o30´ N and only southern group inhabited between 5o30´ and 6o N. Three new Hill Mynah groups were found between 6o and 16o N: with northern group between 9o and 16o N and with southern group between 6o and 9o N. Combination studied of Hill Mynah groups and body mass showed the gradual shift of body mass diffusion in particular areas from north and south to the middle of the country. The relative patterns of phenotypic variation may result from introgressive interbreeding between two original subspecies in a contact zone.