The study provides molecular analyses of fecal microbiota of diarrhea patients infected with four different types of viruses. Fecal specimens from 52 patients with viral diarrhea (13 each of adenovirus, norovirus, rotavirus, and astrovirus) and six healthy individuals were collected and etiological viral agent was confirmed by enzyme immunoassay and specific PCR. To assess the changes in microbial diversity in patients with viral diarrhea, DNA from stool were extracted and characterized by PCR-denaturing gradient gel electrophoresis (DGGE) with universal primers specific for the V3 region of 16S rRNA gene. The strongest bands of the DGGE profiling were excised and sequenced to identify the dominant groups. Bacteroides vulgatus, Bifidobacterium, and Lactobacillus genera were also enumerated by real time PCR. The results revealed that bacterial diversity and similarity in feces from viral diarrhea groups were significantly lower (mean H'/ H'(max) 0.89-0.94, 29-43, respectively) as compared with those of healthy individuals (mean H'/ H'(max) 1.36, 59, respectively). Sequencing of dominant bands affirmed that diarrhea groups were mainly comprised of phylum Firmicutes, such as genera Enterococcus, Peptostreptococcaceae incertae sedi, Streptococcus, Weissella, and Clostridium, and opportunistically pathogenic genus Shigella, while dominant group in healthy individuals was phylum Bacteroidetes. Copy number of Bacteroides vulgatus, Bifidobacterium, and Lactobacillus genera was also reduced significantly in viral diarrhea groups as compared to healthy group. It is concluded that opportunistic pathogens increases, while other species of commensal microbiota decrease significantly in the viral diarrhea patients and dysbacteriosis is dependent on type of virus infection.