Aims: Legionella pneumophila (L. pneumophila) is a human pathogenic bacteria associated with aquatic habitat. It is a causative agent of sever pneumonia known as Legionnaires’ disease (LD). LD among liver transplant recipients (LTRs) is difficult to diagnose with routine methods. The current study was designed to detect Legionella in clinical samples as well as environmental samples in the liver transplant unit of Gastroenterology Surgical Center (GEC), from November, 2014 till June, 2016. Methods: Respiratory, urine and blood samples were collected from 30 LTRs who were hospitalized with signs and symptoms of lower respiratory tract infections. The specimens were screened for L. pneumophila by plate culture method, urinary antigen detection and serological investigation. A total of 40 environmental samples from hospital water and air ventilation system of the same unit were collected and analyzed for the incidence of L. pneumophila. The minimum inhibitory concentration (MICs) of L. pneumophila isolates against 8 antimicrobials were determined. Results: The prevalence of nosocomial Legionella pneumonia was 20%. Six patients were positive for L. pneumophila by culture, among those, urine antigen was detected in five patients and serum investigation yielded positive in three patients. L. pneumophila was recovered from five water samples (12.5%). Azithromycin was found to be the most active against Legionella isolates in vitro. Chlorine (2 mg/L) and superheating (70°C) of hospital water successfully eradicated L. pneumophila. Conclusion: For hospital with transplant units, periodic monitoring of L. pneumophila in hospital water supply and introducing diagnostic tests for LD for patients with nosocomial pneumonia is necessary.