Candida spp. can form biofilms on mucosal surfaces and epithelial cells as well as on devices implanted in the body such as catheters and dentures, which are thought to underlie the most recalcitrant infections. It was aimed to show antifungal and antibiofilm activities of oregano oil (Origanum onites). The antifungal activities of some essential oils were investigated against C. spp. and among them, oregano oil was found to be the most effective oil and further biofilm studies were conducted with it. Oregano oil inhibited biofilm adhesion and formation of C. spp. and mature biofilms and also displayed the ability to reduce biofilm formation when they were allowed to form on surfaces previously coated with oil (up to 50% inhibition rates). In addition, oregano oil was found to be effective against dual biofilms of Candida albicans + Staphyloccocus aureus at different concentrations. This study suggests that O. onites essential oil has useful antibiofilm effects against C. spp. The inhibitory effects of O. onites essential oil, against C. spp., were demonstrated for the first time. It also had antifungal effect on biofilm formation and established biofilm even at MIC level.