Objective：To investigate the correlation of plasma platelet activating factor（PAF） level of patients with sepsis at admission to ICU with their illness severity and prognosis. Methods：Totally 102 patients with sepsis were divided into three subgroups：sepsis group（n=30），severe sepsis group（n=26） and septic shock group（n=46）. All patients were divided into survival group and non-sur－vival group according to their prognosis during the hospital. Forty volunteers were selected as normal controls. The plasma PAF level，serum concentration of inflammatory biomarker procalcitonin（PCT），acute physiology and chronic health evaluationⅡ（APACHEⅡ），simplified acute physiology scoreⅡ（SAPSⅡ） and sequential organ failure assessment（SOFA） scores of patients at admission to ICU were compared. Correlation of plasma PAF level with serum concentration of PCT，scores of APACHEⅡ，SAPSⅡ and SOFA were an－alyzed. Results：Plasma PAF levels were significantly higher in sepsis group，severe sepsis group and septic shock group than in control group（z=-5.424，-5.512，-7.662，P=0.000），and the PAF level was significantly higher in septic shock group than in sepsis and severe sepsis groups（z=-4.559，-3.910，P=0.000） while there was no statistically difference in PAF level between sepsis group and severe sepsis group（z=-0.427，P=0.669）. Plasma PAF level of patients with sepsis was positively correlated with the serum concentration of PCT，scores of SAPSⅡ and SOFA（rs=0.376，0.326，0.483，P=0.000，0.001，0.000），while it was not correlated with APACHEⅡ score（rs=0.143，P=0.152）. Plasma PAF level of patients in non-survival group was significantly higher than that in sur－vival group（z=-3.152，P=0.002）. Receiver operating character－istics（ROC） curve showed that both PAF and APACHEⅡ score could be used as predictors of mortality during the hospitalization（area under the curve=0.708，0.787）. Conclusion：PAF level of patients with sepsis at admission to ICU is essentially and positively correlated with illness severity and prognosis，which could be used to guide the assessment of illness severity and prognosis of patients with sepsis.