Siboglinid worms live on carbohydrates produced by symbiotic bacteria. In this study, α-glucosidase-like activity was detected in the surface of the body and in the trophosome of Oligobrachia mashikoi. The enzyme exhibiting this activity was partially purified by consecutively applying the crude enzyme extract to Con-A-Sepharose and Sephadex-200 HR columns. The enzyme sample thus obtained gave a single activity peak at a position corresponding to 550 kDa in the Sephadex-200 HR gel filtration column. The enzyme was active in the range of pH 6.0–8.0, with a maximum activity at around pH 6.5. It specifically hydrolyzed maltose, and was inhibited by voglibose and miglitol. Moreover, a glucose transporter 2-like protein was detected by immunohistochemical and Western-blotting analyses using anti-rat GLUT2 polyclonal antibody. These results raise the question how this unique species lives.