OBJECTIVE To explore the clinical mansifestations ，endoscopic feature ,high risk factors ,diagnosis and the therapy of the pseudomembranous colonitis. METHOD The clinical data of 28 cases were retrospectively analysed in six yeares.RESULTS All the patients appeared diarrhoea after broad-spectrum antibiotics was used. Advanced age, broad-antibiotic therapy , antibiotic therapy time delayed ,hospital stay delayed ,number of antibiotics used more than one , post- operative procedures were the important clinical risk factors . The colon endoscope appeares the feature of pseudomembranous colonitis. All the patiens were cured by taking Metronidazole、 Vancomvcin or Norvancomycin， after stopping using antibiotics. Vancomvcin and Norvancomycin were more effective than Metronidazole.CONCLUSION Pseudomembranous colonitis is correlation with antibiotics. The pseudomembranous colitis should be first suspected in cases with presumed antibiotic-associated diarrhea having such the risk factors . The cure rates for metronidazole remain low .The best therapy is Vancomvcin and Norvancomycin.