Objectives:To investigate possible sources of Stenotrophomonas maltophilia (S.maltophilia) in the clinical environment.Methods:Different samples were collected from Amol City of Iran.Steps for the identification of S.maltophilia included culturing,biochemical tests,polymerase chain reaction (PCR) of 16S rRNA gene and 23S rRNA gene.In addition,production of melanin pigment and patterns of motility of the bacteria,were also investigated.Results:In our study,20 S.maltophilia strains were isolated from clinical sources,oxygen manometer apparatus of hospitals were 7/1 10 (6.36％),blood was 1/777 (0.13％),sputum was 4/40 (4％),urine was 1/2947 (0.03％),tap water was 1/240 (0.42％) and dental suction was 6/120 (5％).The isolated bacteria showed production of melanin pigment with rates of strong,moderate,weak,and lack of pigment.Types of motilities were seen in isolates.Conclusions:The highest percentage of bacteria is isolated of oxygen manometer system and dental suction,yet has not been reported from oxygen manometer system.These bacteria have also been associated with patients who have respiratory problems,so it is essential for staffs of hospitals to draw attention to this source of bacteria.