This experiment was conducted to investigate the effects of dietary prebiotic xylooligosaccharides (XOS) levels on the intestinal histology, microflora, and disease resistance of the tilapia (〖WTBX〗Oreochromis niloticus×O.aureus〖WTBZ〗). 960 fishes with an initial weight of (5.09±0.12) g were randomly assigned to 6 groups. The fishes were respectively fed a basal diet and 5 diets supplemented with 200, 400, 600, 800 and 1 000 mg/kg XOS, named G0 (control), G200, G400, G600, G800 and G 1000. During 8 weeks feeding period, the number of intestinal microflora was measured every 2 weeks. Midgut was sampled in 4th and 8th week for histology analysis. At the end of feeding, the fish were infected with Aeromonas hydrophila. During 96 hours of artificial infection, the survival rate (SR) was measured. The results showed that in 4th and 8th week, compared with G0, the folding area and the muscle thickness of the intestine in the groups with XOS were significantly higher. Dietary XOS affected significantly the number of intestinal Bifidobacterium and Lactobacillus. Compared with G0, the number of Bifidobacterium in G600 and G800 was significantly higher (P<0.05) in 4th week, in G400 and G600 significantly higher (P<0.05) in 6th week. In 8th week, the number of Lactobacillus in G800 was significantly higher than that in G0 (P<0.05). The number of E. coli in the groups with XOS tended to decrease with the feeding time in creasing, but the difference was not significant (P>0.05). After 96 hours of infection by Aeromonas hydrophila, SR in G0 was 26.7%, and that in the groups with XOS was from 78.3 to 95.0%. The results suggested that the supplementation of XOS into the practical diet could improve the intestinal histology, promote the intestinal bacteria, Bifidobacterium and Lactobacillus proliferation, while decrease the number of E.coli to some extent, and improve the resistance against Aeromonas hydrophila of tilapia (Oreochromis niloticus×O.aureus).