This study analyzes effects of alternative minimum tax (AMT) on firm’s cost of equity capital. Investigating a sample of public firms for 2011-2020, we find that firms paying AMT have a higher cost of equity capital. We also find that the cost of equity capital is higher when the firms paying AMT are non-small and medium-sized enterprises (SMEs). This study contributes to expanding the literature by empirically analyzing how tax regulation affects the capital market. Firms’ behavior motivated by tax regulation could affect the cost of equity capital which is the basis of the firms’ real economic decisions. Thus, the results suggest that tax policymakers make tax regulation more sophisticated.