Abstract: Objective To determine the pulsed-fieldgel electrophoresis(PFGE) patterns of Legionella pneumophila strains isolated from environmental water systems in China.Methods Typing and cluster analysis were performed using pulsed-field gel electrophoresis separately with two restriction enzymes,SfiI and AscI.Results When employing separately SfiI, AscI and combination of the two, PFGE identified 47, 48 and 60 types out of 78 strains of L.pneumophila, respectively, the Simpson difference indexes being 0.9833, 0.9817 and 0.9933.Identical or similar banding patterns were noticed among the isolates from the same water system, though great difference in them was also seen.The presence of strains of identical type was evidenced in the same water system over years.Conclusion PFGE is a highly discriminatory for the subtyping of L.pneumophila.Coexistence of strains derived from multiple clones is evidenced in a same water system, those of certain clones present for years.Predominant clones, observed in environmental water systems, have aroused concerns for further surveillance work.