Breeding territoriality plays a role in determining the reproduction outcome of many passerines species. The spot-mapping was used to estimate the breeding territory size of a territorial male of Oriental Magpie robin (Cospychus saularis) at Dahlia College, Universiti Malaysia Sarawak which is located within Kota Samarahan. It was conducted by mapping the song perching locations established by a marked male. The breeding territory size of the male was estimated to be 0.78 hectares. The data analysis was done using Minimum Convex Polygon (MCP) which was constructed by using Google Earth Pro software. Study on breeding territory size of this bird species is crucial to understand more regarding the breeding behaviour of this species. Data on the behavior of this species could be used for future studies of this bird in Borneo.