Three types of Bifidobacterium thermophilum extract were prepared and fed to 2-wk-old chickens to evaluate their usefulness in enhancing the defense activity of the chickens against pathogenic Escherichia coli. All three preparations resulted in significant reduction (P < 0.05) of E. coli numbers in the lungs of the treated chicken groups compared with the control nontreated group. Besides, improvement in the survival rate was observed in the treated chicken groups, especially the one administered the enzyme-digested B. thermophilum extract sample. Concanavalin A–stimulated lymphocytes from the latter group demonstrated significantly higher proliferation activity compared with those from the control group. These results suggest that oral administration of B. thermophilum preparations may be used to enhance the resistance of chickens against E. coli infection.