To evaluate the effect of probiotics in pigs fed a high fat/high fructose/high cholesterol (obesogenic) diet, three groups of eight recently weaned Ossabaw pigs were maintained on the obesogenic diet and fed 1) 2 x 1010cfu of Bb12 or 2) a probiotic-free vehicle placebo daily, and compared to 3) pigs fed a control basal diet (CD). The obesogenic diet with or without Bb12 increased weight gain, abdominal circumference, total body fat deposition, and serum levels of LDH:HDL cholesterol, and analysis of the intestinal microbiota revealed less bacterial diversity in the lumen and mucosa compared to pigs fed the CD. Notably, morphometric measurements of adipocytes in abdominal fat depots of pigs fed the obesogenic diet and probiotic-free placebo showed a significant increase in size compared to pigs fed CD or the obesogenic diet and Bb12. Systemic leptin levels, however, were significantly increased only in pigs fed the obesogenic diet and Bb12 compared to pigs in the other groups. The juvenile Ossabaw pig fed an obesogenic diet represents a model to evaluate feeding probiotics or other bioactive dietary components on development of obesity, especially since recent studies demonstrated a significant relationship between adipocyte size and % fat gain in the upper body of overfed humans. (Funded by USDA/ARS).