Abstract: In order to explore the relationship between loin muscle thickness（LMT） and host fecal microbes, we measured the LMT adjusted to 100 kg of 91 Duroc pigs. The most extreme 20 individuals were selected based on the LMT, including 10 highest-loin muscle thickness（H＿LMT） pigs and 10 lowest-loin muscle thickness（L＿LMT） 10 pigs. High-throughput sequencing of 16 S rRNA genes was used to analyze the differences of species composition, diversity and predictive function of microorganisms in feces between high and low LMT groups. The results showed that there were two dominant phyla in Duroc pig feces, including Firmicutes and Bacteroidetes, and four dominant genera including Prevotella, Lactobacillus, norank＿f＿ Ruminonoccaceae and norank＿f＿Lachnospiraceae. No significant difference was found in alpha diversity of fecal microbial composition between H＿LMT and L＿LMT groups, and principal coordinates analysis（PCoA） at phylum and genus levels could not be distinguished according to the two groups. However, there were some significant differences in microbial composition between the two groups. At the genus level, the relative abundances of norank＿f＿Enterobacteriaceae, Enterococcus, and Coprobacillus in the feces of the H＿LMT group were relatively higher than those in the L＿LMT group, while the relative abundances of norank＿f＿S24＿7, norank＿o＿Bacteroidales, norank＿f＿Mogibacteriaceae, YRC22, norank＿f＿Peptostreptococcaceae, norank＿f＿Leuconostocaceae, 02 d06 and Corynebacterium in the H＿LMT group were significantly lower than those in the L＿LMT group. Through the functional analysis of KEGG and COG, it was found that the fecal microbes in H＿LMT and L＿LMT groups were highly enriched in the functions of the carbohydrate transport and metabolism, amino acid transport and metabolism, transcription, ribosomal structure and biogenesis. This study provided some basis for exploring the correlation between the composition of porcine fecal microbes and loin muscle thickness, and also provides a theoretical basis for further study of the relationship between intestinal flora and animal growth performance.