ObjectiveTo investigate the characteristics of the composition of intestinal flora and the serum level of endotoxin in cirrhotic patients with malnutrition， and to provide new diagnosis and treatment ideas for improving the nutritional status of patients with liver cirrhosis. MethodsA total of 58 patients with liver cirrhosis who were hospitalized in Department of Gastroenterology， People’s Hospital of Zhengzhou， from March 2021 to November 2022 were enrolled as experimental group （LC group）， and according to the Royal Free Hospital-Nutritional Prioritizing Tool， they were divided into low malnutrition risk group （LC-A group with 28 patients） and moderate/high malnutrition risk group （LC-B group with 30 patients）； 25 individuals who underwent physical examination during the same period of time were enrolled as control group （HC group）. Peripheral blood and feces samples were collected from all subjects. The limulus amebocyte lysate gel method was used to measure the concentration of endotoxin in peripheral blood， and high-throughput sequencing and bioinformatics analysis were used to investigate the characteristics of intestinal flora. The independent-samples t test was used for comparison of normally distributed continuous data between two groups； a one-way analysis of variance was used for comparison between multiple groups， and the least significant difference t-test were used for further comparison between two groups. The Mann-Whitney U test was used for comparison of non-normally distributed continuous data between two groups， and the Kruskal-Wallis H test was used for comparison between multiple groups. The chi-square test was used for comparison of categorical data between groups. The Spearman test was used for correlation analysis. ResultsThere were significant differences between the three groups in the levels of alanine aminotransferase （H=7.054， P<0.05）， gamma-glutamyl transpeptidase （H=9.644， P<0.05）， albumin （Alb） （F=32.768， P<0.05）， total bilirubin （TBil） （H=20.980， P<0.05）， and serum endotoxin （F=108.672， P<0.05）. There was a significant difference in Chao1 index between the three groups （F=5.110， P=0.008） and between the HC group and the LC-B group （P<0.05）. Compared with the HC group， the LC-A group and the LC-B group had significant reductions in Chao1 index and Shannon index， and there was a significant difference in Chao1 index between the HC group and the LC-B group （P<0.05）. At the phylum level， the intestinal flora in each group was mainly composed of Bacteroidota， Firmicutes， Proteobacteria， and Actinobacteriota， accounting for more than 95% of all phyla， and there was a significant difference in the relative abundance of Firmicutes between the HC group and the LC-B group （P<0.05）. Serum endotoxin was significantly negatively correlated with Ruminococcaceae （r=-0.420， P=0.007）， and spirochete was significantly positively correlated with TBil （r=0.419， P=0.007） and was significantly negatively correlated with Alb （r=-0.492， P=0.001）. ConclusionThere are unique changes in intestinal flora in cirrhotic patients with malnutrition， and differentially expressed flora are associated with endotoxemia. Improving intestinal microecology in liver cirrhosis may help to improve nutritional status.