Objective The changes of antimicrobial activities of Curcuma longa and Zingiber Purpureum before and after illumination were studied. Methods Disk diffusion test was applied to detect the antimicrobial activity of Curcuma longa and Zingiber Purpureum extracts against 20 kinds of microbial pathogens before and after illumination. TLC was applied to detect peroxide products and reductive products in the extracts of Curcuma longa and Zingiber Purpureum after illumination, by which whether the photochemical reaction occurred were determined. Results The antimicrobial activities of the two extracts increased significantly after illumination. New products were detected in the two extracts after illumination, which indicated that the photochemical reaction had occurred. Conclusion Under the catalysis of curcuminoids, some components in Curcuma longa and Zingiber Purpureum underwent photochemical reaction under illumination. As a result, components with higher antimicrobial activity were generated.