Purpose - Prior studies have found that the characteristics of managers, corporate governance structure, corporate social responsibility and so on affect firm value. This study explores whether managerial overconfidence affects firm value through empirical analysis. Design/methodology/approach - Korean-listed non-financial companies from 2011–2017 are collected as the research sample. Firm value is measured by Tobin's Q, and managerial overconfidence is measured using a composite index encompassing various financial data. OLS and fixed effect model are used to investigate the relationship between managerial overconfidence and firm value. Findings - Managerial overconfidence is positively associated with firm value. Additional analysis reveals the following: (1) In the three subsamples of large, backbone, and small- and medium-sized enterprises, managerial overconfidence is beneficial to firm values. (2) Managerial overconfidence increases firm value on the t+1 year. Research implications or Originality - We use a comprehensive index with higher trust and feasibility to measure manager overconfidence and empirically confirm that managerial overconfidence can become a factor to improve firm value. Thus, it is necessary for shareholders to adopt an objective and neutral attitude and reasonably understand the psychological characteristics of managers when selecting CEOs. In addition, it is necessary to continue to optimize the measurement method of managerial overconfidence.