Objective To explore the contamination by Legionella pneumophila in cooling water of centralized air condi-tioning system in hospitals and hotels.Methods In Aug2001,the water from cooling towers of centralized air conditioning sys-tems in4hospitals and2hotels were sampled in W city.The membranes filtering the cooling water samples were treated by hy-drochloric acid.After treatment,the mixed treated solution was inoculated into GVPC plate and cultured in candle jar.The susepectable colonies were identified by biochemical test,serological test and PCR test respectively.Results5strains of L pneu mophila in cluding3strains of Lp1type and2strains of Lp5type were isolated from water samples of the cooling towers of centralized air conditioning systems in2hospitals and one star-grade hotel in W city.Conclusion The contamination by le-gionella in water of cooling tower of centralized air conditioning system in hospitals and hotels should be monitored closely.