AIM: To explore the antitumor mechanisms of bifidobacteria adolescence in vivo. METHODS: The activity of NF-?B and its inhibiting protein I ?B? of large bowel carcinoma tissues was detected by using laser scanning confocal microscope and immunohistochemistry. RESULTS: The positive cell density of NF-?B of large bowel carcinoma transplantation tumors in bifidobacterium injection group was markedly lower than that in tumor control group( P