The effects of pollens of Bt Chinese cabbage (Brassica campestris), expressing the insecticidal protein Cry1Ac toxin (Bt Chinese cabbage) on Bombix mori larvae, were determined in laboratory studies. When reared on an artificial diet containing pollens of Bt Chinese cabbage, decreased survival rate and body weight of B. mori larvae were observed. ELISA test using Cry1Ac-antibody implied that the Cry toxin was detected not only in the whole body and alimentary canal but also in the hemolymph and remaining body parts, suggesting that the ingested Cry1Ac protein is distributed inside the body through epithelial membrane of the midgut of B. mori. Taken together, it was suggested that the pollens of Bt Chinese cabbage adversely affect non-target insect B. mori larvae.