In financial markets, stock prices not only reflect firm-specific information but also convey industry conditions, growth opportunities, and market expectations. Drawing on the informational role of financial markets and peer learning theory, managers use information embedded in stock prices and peer firms' performance when making investment decisions. This study investigates the effect of peer firms' stock prices on corporate investment and the moderating roles of peer performance and managerial overconfidence. The hypotheses are tested using a sample of 144 firms listed on the Tehran Stock Exchange during 2015–2024, employing multivariate regression models with year and industry fixed effects. Managerial overconfidence is measured using two proxies: overinvestment and capital expenditures. The findings indicate that peer firms' stock prices have a positive and statistically significant effect on corporate investment, while peer performance strengthens this relationship. Furthermore, the moderating role of managerial overconfidence depends on the proxy used. Specifically, managerial overconfidence, when measured by capital expenditures, positively and significantly moderates the relationship between peer firms' stock prices and corporate investment, whereas this effect is not statistically significant when overconfidence is measured by overinvestment.