MRSA adheres to and proliferates in damaged tissue, implanted medical and prosthetic devices, and is capable of forming biofilms [7, 8]. Biofilms constitute bacterial communities that form on the surface of living and nonliving substances. Biofilms are surrounded by a self-produced extracellular matrix that consists of polysaccharides and proteins. These biofilms are very difficult to remove and are a cause of intractable infection. Biofilms formed on the surface of implanted medical devices cannot be removed by antibiotic injection and can only be removed by surgery in most cases. After excising the peripheral tissues of biofilms, antibiotics need to be utilized for a long period of time [7, 8]. The most well-known method for analyzing biofilm formation is a tissue culture plate assay method [9]. In this study, biofilm formation was observed via safranin staining. The result showed that A. princeps inhibited biofilm formation of MRSA at concentrations of 1–8 mg/mL. Similar results were observed when MRSA biofilm formation was measured by SEM. A previous study reported that biofilm culture and planktonic culture showed different physiological characteristics, even when the same types of bacteria were cultured. Biofilm formation reportedly increases the immune response of bacteria and their resistance to antibacterial substances [17]. However, comparing biofilm culture data and planktonic culture data in the present study, there were no considerable differences in their resistance to ethanol extract of A. princeps between the two groups.