AIM: To investigate the effects of psychological stress on ulcerative colitis rats and to explore the mechanisms of this;meanwhile to investigate the effects of anxiolytic drug on symptoms of ulcerative colitis rats under psychological stress and the mechanisms of it.METHODS: eighty male Wistar rats were randomly divided into four groups(n=20): UC control group;UC stress group;UC+clonazepam group;UC stess+clonazepam group.After UC model was established with immunization,these rats were fightened by cat to set up psychological stress model.During establishing stress model,each groups were respectively received physiologic saline or clonazepam by intragastric administration.After 15d treatment,all rats were sacrified simultaneously.Colon mucosal inflammationand damage were assessed by measuring colon mass,morphologic damage score,colonic MPO and NO activity levels.Morphologic damage score was examined under microscope.Colonic MPO and NO was measured by spectrophotometric method.Serum hydrocortisone was determined by radioimmunoassay(RIA).RESULTS: Morphologic damage score,colonic MPO and NO,serum hydrocortisone of UC stress group were significantly increased compared with those of UC control group;morphologic damage score,colonic MPO and NO,serum hydrocortisone of UC+clonazepam group were decreased markedly vs UC stress group;Little difference was observed between UC+clonazepam group and UC control group.CONCLUSION: Psychological stress can aggravate symptoms of UC.Although benzodiazepine have no anti-inflammatory action,it relieve effects on internal organs of psychological stress and aggravation of symptoms of UC by to effect limbic system and formatio reticularis.