Baseline data on the distribution patterns of animals disclose the dynamic function of habitat use as it relates to the accessibility of prey, social interactions, predator-prey interactions, and inter-habitat-patch mobility. Differentiated distribution patterns in sympatric animal species may imply a spatial-partitioning of habitat use. This study used minimum convex polygon and kernel density estimate techniques to measure the extent of occurrence and core habitat of the Indo-Pacific humpback dolphin (Sousa chinensis), Irrawaddy dolphin (Orcaella brevirostris), and Indo-Pacific finless porpoise (Neophocaena phocaenoides) in the central-western Gulf of Thailand. For the three cetacean species, their extent of occurrence greatly overlapped, while their core habitats were nearly disjointed, with minor overlap. Principal component analysis and discriminant analysis revealed significant differences in the habitat characteristics inside core habitats, which imply geographic separation of foraging patches between Irrawaddy dolphins, humpback dolphins, and finless porpoises. Based on the core habitat identification, we propose precautionary actions to maintain the habitat condition and integrity inside the core habitats for the three sympatric cetacean species, including revisiting the regulations and mitigation rules for local fisheries and dolphin-watching tourism; re-routing the ferry lanes to avoid the core habitats; and avoiding large-scale coastal modification, such as land reclamation and embankment, in the waters near core habitats.