ObjectiveTo investigate the clinical characteristics and pathogenic microorganisms in culture-positive sepsis, to identify its risk factors, and evaluate the prognosis on polymicrobial infection in intensive care unit (ICU).Methods A descriptive retrospective study was conducted. Clinical data of patients aged≥ 18 years, diagnosed as culture-positive sepsis, and admitted to six ICUs of Guangdong General Hospital from October 12th, 2012 to December 1st, 2014 were enrolled. Based on the number of isolated pathogens, patients were divided into polymicrobial infection group (≥two pathogens) and monomicrobial infection group (one pathogen) to investigate the clinical characteristics of patients with culture-positive sepsis and the causative pathogens. Multiple logistic regression was conducted to identify the risk factors for polymicrobial infection. Kaplan-Meier curve was plotted to analyze a 90-day survival rate from the onset of positive blood culture.Results 299 patients with positive blood culture were enrolled. A total of 450 strains of pathogens were isolated including 246 gram-positive cocci (54.67%), 167 gram-negative bacilli (37.11%) and 37 fungi (8.22%). Ninety-one patients had polymicrobial infection, and 208 with monomicrobial infection. Compared with monomicrobial infection group, patients suffering from polymicrobial infection had more advanced age (years: 73.19±18.02 vs. 60.83±18.06,t = -5.447,P = 0.000), also with higher incidence of cerebrovascular diseases [39.56% (36/91) vs. 17.79% (37/208),χ2 = 16.261,P = 0.000] or chronic renal insufficiency [15.38% (14/91) vs. 7.21% (15/208),χ2 = 4.828,P = 0.028], higher incidence of recent hospital stay (≥2 days) within 90 days [73.63% (67/91) vs. 61.54% (128/208),χ2 = 4.078,P = 0.043], longer mechanical ventilation duration [days: 4 (0, 17) vs. 1 (0, 6),U = 7 673.000,P = 0.006], longer length of hospital stay before blood was drawn for culture [days: 21 (7, 40) vs. 9 (3, 17),U = 6 441.500,P = 0.006], and higher incidence of pre-admission intravenous use of antibiotics [84.62% (77/91) vs. 66.83% (139/208),χ2 = 9.989,P = 0.002]. Multiple logistic regression analysis showed that advanced age [odd ratio (OR) = 1.032, 95% confidential interval (95%CI) = 1.015-1.050,P = 0.000], cerebrovascular diseases (OR = 2.247, 95%CI = 1.234-4.090,P = 0.008), prolonged mechanical ventilation (OR =1.041, 95%CI = 1.014-1.069,P = 0.003), and recent hospital stay (≥2 days) within 90 days (OR = 1.968, 95%CI =1.079-3.592,P = 0.027) were the independent risk factors for polymicrobial infection. In the polymicrobial infection group, the length of ICU stay [days: 46 (22, 77) vs. 13 (7, 22),U = 3 148.000,P = 0.000] and hospital stay [days:81 (47, 118) vs. 28 (17, 46),U = 3 620.000,P = 0.000] were significantly longer, and the ICU mortality [65.93%(60/91) vs. 43.75% (91/208),χ2 = 12.463,P = 0.000] and hospital mortality [68.13% (62/91) vs. 45.67% (95/208),χ2 = 12.804,P = 0.000] were significantly higher, and on the other hand the 90-day survival rate was significantly lower than that in the monomicrobial infection group (χ2 = 8.513,P = 0.004).Conclusions The most common pathogen of ICU sepsis is gram-positive cocci. Independent risk factors for polymicrobial infections were found to be advanced age, occurrence of cerebrovascular disease, prolonged mechanical ventilation, and recent hospitalization. Polymicrobial infection is associated with longer length of ICU and hospital stay, as well as higher mortality.