Objective: To study the relationship between colonic microflora and lactose intolerance symptoms. Methods: 42 volunteers were chosen and divided into lactose intolerance(LI) and lactose malabsorption groups according to the 25 g lactose-challenge test and symptoms questionnaires. Fresh fecal samples were collected from the volunteers, and the fluorescence in situ hybridization (FISH) technique with group-specific 16S rRNA-targeted oligonucleotide probes was used to quantify the total bacterial and predominant groups of bacteria in fecal samples. The effect of milk-drinking habit on the number of Bifidobacteria was analyzed. Results: It showed that there was significant difference in the number of total bacteria and Bifidobacteria between lactose intolerance groups and malabsorption group(P