Variation at 14 microsatellite loci was surveyed in 205 populations of chum salmon ( Oncorhynchus keta (Walbaum in Artedi, 1792)) from British Columbia to determine population structure and the possible application of microsatellites to estimate stock composition of chum salmon in mixed-stock fisheries. The genetic differentiation index (FST) over all populations and loci was 0.016, with individual locus values ranging from 0.006 to 0.059. Sixteen regional stocks were defined in British Columbia for stock identification applications. Analysis of simulated fishery samples suggested that accurate and precise regional estimates of stock composition should be produced when the microsatellites were used to estimate stock compositions. The main stocks that constitute the October 2007 samples of migrating chum salmon through Johnstone Strait in southern British Columbia were Fraser River (45%–64%), southern British Columbia mainland (22%), and east coast Vancouver Island (13%–28%), within the range of those to be expected in samples from Johnstone Strait. Microsatellites have the ability to provide fine-scale resolution of stock composition in British Columbia coastal fisheries.