Functional foods are important sources of probiotic delivery, mainly by fermented milk products. The physiological benefits attributed to bifido bacteria are their abilities to interfere with the adhesion of pathogenic species to surfaces of intestinal cells, and to enhance host´s immune function through their metabolic activities. However, the effect of technological approach – fermentation or addition of probiotic in milk, and its efficacy in health are rarely taken into consideration. Hence, fermented or unfermented milks using Bifidobacterium animalis subsp. lactis HN019 were administered to BALB/c mice for 14 days. After that, the architecture of the gut was histologically investigated, and the related immune cells were examined by flow cytometry and immunofluorescence. Increase in mucus and cellularity production, changes in immune pattern and preservation of mucosal epithelia in health BALB/c mice were observed, just in fermented milk group. This suggested that changes in functionality of bifidobacteria and/ or the metabolites produced by the fermentation process are the keys to improving beneficial effects in the host of gut mucosa.