The ability of biofilms formation was studied by utilizing fifty Pseudomonas aeruginosa strains isolated from both environmental and hospital samples. The support utilized for strains fixation was in polystyrene and contained two liquid media: Luria-Bertani and Mineral Medium supplemented with Hexadecane as the sole source of carbon and energy. The results obtained showed that the Biofilms-forming ability depend on both media carbon source and the P. aeruginosa strain variety. When the carbon source is hard to degrade or toxic, like hexadecane or derived substrates, the formed biofilms presented a high density; however, when the carbon is easy to degrade by the strains; like that one of L.B medium, the formed biofilms have a slight density. Furthermore, this density is also influenced by the strains although they belonged to the same species; at this purpose, the ERIC - PCR analysis, showed that P. aeruginosa strains studied are various because their profil ERIC present a percentage of similarity which not exceeds 60%.