###### Abstract  
The aim of this study was to investigate the antifungal and antioxidant activities of _Chmanacyparis obtuse_ (_C. obtusa_) extract (COE) against _Candida albicans_ (_C. albicans_). Methods: The antioxidant activity was determined using three methods based on 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) scavenging, total polyphenol measurement, and total flavonoid measurement. In addition, the survival rate of human keratinocytes (HaCaT) was checked to confirm their stability. A one-way ANOVA also confirmed the antifungal activity of COE against C. _ albicans_ and its proliferative effect on HaCaT cells. In addition, to confirm the difference between each group, the Tukey HSD test was performed as a post hoc analysis, and the significance level was set at 0.05 as a two-tailed test. Results: COE was found to contain 424.150 mg GAE/g of polyphenols, 127.566 mg CE/g of flavonoids, and 83.594% of radical scavenging activity. Furthermore, 30 mg/mL of this extract exhibited complete antifungal activity. In addition, a noticeable killing effect on C. _ albicans_ was observed as the concentration of the extract increased. For instance, at a 2.5 mg/mL dosage of COE, HaCaT cells were safe, but C. _ albicans_ showed a distinct antifungal effect. Conclusions: COE has antioxidant and antifungal activity, so it has a high potential as an effective natural antifungal agent. Therefore, oral gargle containing COE is expected to be a safe and effective treatment in oral candidiasis in clinical practice. Keywords:antioxidant; antifungal effect; _Candida albicans; Chamacyparis obtuse_; toxicity +
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susceptibility to antimicrobials and phagocytosis decreases drastically [8]. Importantly, in addition to _Candida_'s pathogenic factors and interactions with the host immune system, it is now acknowledged that the bacterial component of the oral microbiome plays an important role in the development and exacerbation of oral candidiasis [9]. Among the oral bacterial flora, streptococci are important for the colonization of _C. albicans_. Therefore, the interaction between _C. albicans_ and streptococci is known to show a synergistic effect as an oral fungus-bacteria interaction. Specifically, interactions with _Streptococcus oralis_, _Streptococcus mtius_, _Streptococcus gordonii_, and _Streptococcus mutans_ have been reported to adhere to the hyphae of _C. albicans_[10]. By using the lactic acid produced by streptococci, _C. albicans_ lowers the partial pressure of oxygen to a level favorable to conditional streptococci [11]. In an experimental study, it was reported that _C. albicans_ caused occlusal caries because, similar to S. mutans, _C. albicans_ has the ability to produce and withstand acid. Therefore, the potential role of _C. albicans_ in caries development through physical and metabolic interactions with S. mutans has been confirmed through several lines of evidence [12]. Additionally, exoenzyme glucosyltransferase B (gtfB) produced by S. mutans has been shown to be deposited on the surface of _C. albicans_ hyphae, helping the fungus attach to oral surfaces [13]. In this respect, _C. albicans_ can interact with oral bacteria and cause more serious diseases. Oral candidiasis does not cause problems in healthy populations [1], but it primarily affects infants and the elderly and causes opportunistic infections in individuals with prolonged antibiotic use or immunocompromised status [14]. Therefore, antibiotics should not be used for a long period of time for the purpose of preventing oral infectious diseases or continuously suppressing oral pathogens. Accordingly, natural extracts, instead of synthetic chemical ingredients, are recommended in mouthwashes to control pathogens while maintaining oral microflora [15]. Thus, natural extracts have grown in popularity in recent years [16] as more research has been conducted. _Chameucyparis obtusa_ (_C. obtuse_) is an evergreen conifer native to East Asia, including Japan and Taiwan, and a member of the _Cupressaceae_ family.