The effect of feeding a novel dietary antigen on the gastrointestinal tract function of specific pathogen free cats was determined using breath hydrogen xylose (BHX) test and bacteriological culture of duodenal aspirates collected during endoscopy. These functions were monitored of absorptive ability of feeding cycle for detection after each gastrointestinal tract as well as the effect of novel dietary antigen on change of intestinal flora. Breath hydrogen xylose test results were not suggestive of consistent mal-absorption in the treatment group due to introducing ovalbumin into their diet. After the start of ovalbumin feeding, the aerobic bacterial count significantly increased in all cats (P<0.05). A remarkable change in quality of bacteria was also evidenced in duodenal aspirates collected from all cats after introducing ovalbumin into the cats' diet. Anaerobic bacterial quality and quantity changes were not significant (P>0.05). In conclusion, the results of this study demonstrates that aerobic bacteria change significantly in quality and quantity in the small intestine of cats after introducing a novel antigen into their diet. Such changes might have an effect on the gut associated lymphoid tissue response which could be involved in the pathogenesis of enteropathies in cats,