Research on the interaction between dietary vitamins and intestinal bacteria is poorly understood. To investigate the effect of dietary vitamins on the cecal bacterial communities, 2 bacterial 16S rRNA gene clone libraries were constructed from pooled PCR products obtained from the cecal digesta of 28-d broilers fed diets with vitamins (V) at the NRC level or with no vitamins (NV). The results showed that BW gain and average feed intake of V broilers was significantly higher (P < 0.01) than NV broilers, whereas the feed/gain ratio was significantly lower (P < 0.01) in V broilers. A total of 188 and 185 clones were sequenced for the NV and V broilers, respectively. Sequence identity criterion of 98% was used to assign sequences to operational taxonomic units (OTU). Clones from the NV group broilers were assigned to 14 OTU, with 33% clones affiliated with the genus Clostridium, 19% affiliated with the genera Escherichia/Shigella, 14% affiliated with the genus Bacteroides, and the remaining clones (34%) affiliated with 5 other bacterial genera (Faecalibacterium, Parasporobacterium, Ruminococcus, Streptococcus, and Subdoligranulum). Clones from the V group broilers were assigned to 23 OTU, with 46% of the clones affiliated with the genus Clostridium, 11% affiliated with the genus Fecalibacterium, and the remaining clones (43%) affiliated with 8 other genera (Anaerofilum, Lactobacillus, Anaerotruncus, Oscillibacter, Alistipes, Gracilibacter, Acetivibrio, and Haloplasma). Three OTU assigned to Clostridium, Faecalibacterium, and Ruminoccus were shared between the 2 libraries. Shannon diversity index showed the V broilers exhibited significantly higher bacterial diversity (P = 0.05), and Libshuff analysis indicated that the community structure between the 2 groups was significantly different (P < 0.0001). These results suggest that lack of dietary vitamins can increase the ratio of facultative pathogenic bacteria and decrease the diversity of bacteria in the cecum of broilers. Our results provide new leads for further investigations on the interaction between dietary vitamin additives and the gut health of broilers.