The relationship between Streptococcus (St.) bovis endocarditis and colon cancer is well known. In St. bovis, the biotype I strain (formerly, St. gallolyticus) produces tannase that degrades tannins. The aim of this study was to investigate the association of tannase-producing bacteria with colon cancer, and to identify the major tannase-producing bacteria and the gene involved.Tannase-producing bacteria were isolated in tannic acid-treated selective agar medium from feces and rectal swabs of 357 patients who underwent colon endoscopy from 1999 to 2004.Tannase-producing bacteria were isolated more frequently from the colon cancer group (24.3%) than from the adenoma or normal groups (14.4%; P < 0.05). S. gallolyticus, Staphylococcus (S.) lugdunensis, Lactobacillus (L.) plantarum, and L. pentosus were all identified as tannase-producing bacteria. Of these, S. lugdunensis was significantly isolated from the advanced-stage cancer group (22.2%; P < 0.001) more than from the early-stage cancer (8.6%) or adenoma (4.9%) groups. The gene (tanA) for tannase in S. lugdunensis was cloned and sequenced. The tanA gene was associated with all S. lugdunensis but not with other bacteria by Southern blotting and polymerase chain reaction.Tannase-producing S. lugdunensis is associated with advanced-stage colon cancer, and the tanA gene is a useful marker for the detection of S. lugdunensis.