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The short mackerel Rastrelliger brachysoma (Bleeker, 1851) is a commercially important fish in the Gulf of Thailand (GoT). The management strategy for this species in the entire GoT is based on the single-stock approach, which may not be efficient or effective. This study aims to identify the stock structure of short mackerel in the GoT. A total of 55 samples of short mackerel were collected throughout the GoT, sexed, weighed and measured. The pair of sagittal otoliths were removed from individual fish. The left sagittae were used for stock identification via microchemistry elements. The microchemical composition of the otoliths from four locations (Eastern, Upper, Central and Lower GoT) was different (MANOVA, P < 0.01) for both sexes. The linear discriminant function analysis (LDFA) using eight microchemical elements in the edge zone showed high classification accuracy of short mackerel with regard to their sampling location (89% for males and 79% for females). The LDFA results also showed high classification accuracy in both sexes (more than 85%) and indicated that there were four short mackerel stocks in the GoT. The right sagittae, meanwhile, were used for fish ageing. Results showed that the adults had resided in the stock more than 50% of their life before being captured. [ABSTRACT FROM AUTHOR]