Abstract: OBJECTIVE To understand the clinical characteristics and molecular epidemiological characteristics of K1 serotype Klebsiella pneumoniae (K1-Kpn). METHODS From Jan 2015 to Dec 2015, totally 331 strains of non-repetitive K.pneumoniae were isolated from various specimens, the strains were identified by using Vitek-2 Compact automatic microorganisms analysis system, and the drug susceptibility was analyzed.The hypermucoviscous phenotypes of the strains were detected by ‘string test'; the 6 types of hypervirulent capsular serotypes, 7 types of common virulence genes and 17 types of common antimicrobial resistance genes were detected by using PCR method, the molecular epidemiological characteristics of K1-Kpn were analyzed with the use of multilocus sequence typing (MLST).The clinical characteristics such as the average age, average acute physiology and chronic health evaluation (APACHE) II score, average hospitalization duration and rate of ICU stay were observed and compared with 40 patients with non-K1-Kpn infection. RESULTS Totally 37 strains of K1-Kpn were isolated, the positive rate of HM test was 72.97%, the carrying rates of the 7 common virulence genes varied from 91.89% to 100.00％.The average age of the patients with K1-Kpn infection was (55.43±16.10) years old, the average age of the patients with non-K1-Kpn infection (43.43±14.2) years old, and there was significant difference (Z=-5.412,P=0).The APACHE Ⅱ score of the patients with K1-Kpn infection was (27.72±8.53) points, the APACHE Ⅱ score of the patients with non-K1-Kpn infection (18.63±7.29) points, the difference was significant (Z=-14.388,P=0).The average hospitalization duration of the patients with K1-Kpn infection was (53.7±27.4) days, the patients with non-K1-Kpn infection (10.2±8.4)days, and there was significant difference (Z=-4.311,P=0).The ICU isolation rate of the patients with K1-Kpn infection was 45.95%(17/37), the patients with non-K1-Kpn infection 20.00%(8/40), the difference was significant(χ²=5.9,P＜0.05).The strains remained highly susceptible to commonly used antibiotics, and the detection rate of ESBLs-producing strains was 13.5%(5/37).The PCR result showed that there were 4 (10.81%) SHV type β-lactamase-producing strains, 4 (10.81%) TEM type strains and 14 (37.84%) CTX-M type; there were 13 (35.14%) strains carrying with PMQR gene and 1 strain carrying with 16 SrRNA methylationase gene, the carbapenemase gene was not detected.The MLST indicated that ST23 was the predominant sequence type. CONCLUSION The K1-Kpn strains carry with a variety of virulence genes, the drug resistance mechanism is closely associated with the β-lactamse genes, the ST23 is the major clinical epidemic strain.As for the middle-aged cardiovascular and cerebrovascular diseases patients complicated with pulmonary infection, it is necessary to actively prevent the K1 type strain infection and control the spread.