AbstractAfter illumination with white, linearly polarized light (WLPL), cyclodextrin glycosyltransferase produced mixture of α‐, β‐, and γ‐cyclodextrins (CD) with higher overall yield than did that enzyme when nonilluminated. The illumination also influenced the ratio of those CD and that effect depended on concentration of enzyme and illumination time. At a high enzyme concentration (0.64 U/cm3), regardless the illumination time, formation of β‐CD predominated. The highest yield of β‐CD was afforded after 1 h illumination and 2 h illumination led to a significant increase in the yield of γ‐CD. Three‐month storage of enzyme illuminated with WLPL did not reduce its enhanced activity. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009