Southeast Asia has been a very dynamic economic region. Its economic openness to the World is reflected not only in their robust economic growth but also in effects of World economy on each country in the region. In an ever changing business environment, a firm has to decide an optimal capital structure from which the firm builds a sustainable foundation to support its investments and operation. The goal of this research is to investigate the determinants of corporate capital structures of listed firms in Southeast Asian countries between 2006 and 2015: Vietnam, Thailand, Indonesia, Malaysia, Indonesia, and Singapore. The data for research are collected from Thompson Innovation database. In this article, the authors use a combination of qualitative and quantitative research methods to conduct an individual country model employing ordinary feasible generalized least square (FGLS) model and feasible generalized least square (FGLS) with fixed effects model. Empirical evidence supports neither the pecking-order model nor the trade-off model as the better framework to understand the capital structures of firms in Southeast Asia between 2006 and 2015 and confirms the similarity in leverage decisions and determinants of capital structures of firms in the region.