In the summer of 1999, disease symptoms of unknown origin were observed on onion bulbs in the fields and storage houses in Korea. Water soaked and very pale brown lesions appeared on the internal scales of diseased onion bulbs; they enlarged and extended to external scales with an associated sour smell. Bacterial soft rotting was more common than scale discoloration. This symptom was more pronounced at the neck end. From these lesions, we isolated two bacterial strains (designated CH1, CH2). Inoculation of bacterial isolates into onion bulbs yielded characteristic water-soaked symptoms which were distinguishable from those of the soft rot well known to onion growers. Inoculation of onion leaves and seed stalks produced white, oblong, slightly sunken and elongated spots. These symptoms started to appear 48 h after inoculation and leaves were completely killed within a week. Results of Gram stain, staining of flagella and biochemical tests identified these isolates as Burkholderia gladioli pv. alliicola. This was confirmed by pathogenicity, physiological and biochemical characteristics, an analysis of the 16S rRNA gene sequences and fatty acids profile. This is the first report of this bacterium in Korea.