It has been shown recently that signal-mediated interactions between the opportunistic pathogens Pseudomonas aeruginosa and Candida albicans affect virulence features in both organisms. It has been emphasized that the anti-candidal activity of P.aeruginosa is especially due to its pyocyanin pigment. The structure and the properties of monospecies biofilms and their role in infectious disease have been extensively studied. However, there are only few studies on interactions between P.aeruginosa ye Candida spp. in mixed biofilms. Therefore, in this study, the investigation of anti-candidal activity of P.aeruginosa against Candida spp. and the effect on C.albicans biofilm were aimed. A total of 58 P.aeruginosa strains isolated from several clinical specimens and one of each C.albicans ATCC 90028, C.parapsilosis ATCC 22019, C.glabrata ATCC 90030 and a C. tropicalis clinical isolate were included in the study. The anti-candidal activity of P.aeruginosa strains were investigated on Sabouraud dextrose agar using Kerr's method. The absence of the growth of Candida strains were evaluated as total inhibition. The effect of two P.aeruginosa strains showing total inhibition and one isolate without inhibition effect on C.albicans biofilm was investigated by microplate method. For the evaluation of monospecies or mixed species biofilms of Pseudomonas and C.albicans, the number of colony forming units (cfu/ml) after 90 minutes (adhesion phase), 24 hours and 48 hours (biofilm phase) incubation were determined. Then, cfu numbers of monospecies and mixed species of Pseudomonas and C.albicans were compared. Total inhibition rates of Pseudomonas strains against C.albicans, C.tropicalis, C.glabrata and C.parapsilosis were determined as 63.8%, 75.9%, 65.5% and 72.4%, respectively. A significant reduction was determined in cfu/ml numbers of mixed species of Pseudomonas and C.albicans compared to cfu numbers in monospecies biofilm after 90 minutes, 24 hours and 48 hours (p < 0.05). In addition to the inhibitory effect of P.aeruginosa on Candida growth, in a dual species environment both organisms mutually suppressed eachothers' biofilm development quantitatively. These findings indicated that molecular basis of signal-mediated interaction between Pseudomonas and Candida spp. should be clarified for better understanding of the pathogenesis of mixed bacterial-fungal infections.