This study addressed the question of whether capital structures across countries are converging. For this purpose, the capital structures of manufacturing firms in major OECD countries over the past 20 years were selected as the subject of analysis. Initially, the graphical trends in their debt ratios were observed to recognize the possibility of convergence over time. Subsequently, to statistically test the capital structure convergence hypothesis, the concepts of σ-convergence and β-convergence were introduced and newly defined to test this hypothesis. The test results showed that the σ-convergence results varied depending on the sample used, and in the case of β-convergence testing for individual countries, the hypothesis that Japan's capital structure converges toward the average level was accepted as statistically significant. This study contributed to corporate finance research in that it moved beyond the traditional framework of examining the existence of an optimal capital structure at the micro firm level and explained the discussion of economy-wide capital structure transitions based on the concept of convergence.