<p>Authenticity is a crucial concept in psychological well-being, with growing scientific significance and social relevance. One psychological factor associated with authenticity is self-consciousness. However, the literature contains few and inconsistent empirical findings regarding the relationship between different self-consciousness dimensions and authenticity. This study examines how self-consciousness dimensions relate to authenticity among young adults in Turkey, with a focus on the role of free will belief. Using Existential Psychotherapy Theory, the research examined the relationship between self-consciousness and authenticity, and how free will belief relates to it. 446 young adults in Turkey participated in the study via an online survey. Structural equation modeling results showed that internal state awareness and appearance consciousness were positively associated with authenticity, while style consciousness and social anxiety were negatively associated with it. Free will belief was statistically associated with the relationships between internal state awareness-authenticity (partial mediating), appearance consciousness-authenticity (partial mediating), and style consciousness-authenticity (partial mediating). These findings suggest that free will belief may be related to the effect of self-consciousness on authenticity. Higher levels of internal awareness and appearance consciousness, along with stronger free will belief, were associated with higher authenticity scores. Conversely, higher style consciousness, along with lower free will belief, was associated with lower authenticity scores. The results suggest that further investigation into the ways in which internal awareness, expectations about external appearance, and free will belief relate to authenticity, may be useful in clinical practice. These findings are related to the propositions of Existential Psychotherapy Theory and shed light on the role of self-consciousness dimensions and free will belief in understanding authenticity.</p>