Capital structure is increasingly important in determining the optimal combination of funding for investment needs that can increase firm value from profitability. The study aims to examine the effect of capital structure on profitability of electricity companies in Southeast Asia. The study used multiple regression model represented by pooled least square to calculate 48-panel data from the annual financial report during the time period of 2009-2016. We utilized short-term debt to total assets (STD), long-term debt to total assets (LTD), total debt to total assets (TD), and debt to equity ratio (DER) as proxies of capital structure (independent variables). Operating income margin (OIM), return on asset (ROA), and return on equity (ROE) were the profitability proxies (dependent variables). Firm size and firm age were used as control variables in the study. The results of this study indicate that STD and LTD have a negative relationship that consequently has significant effect on LTD and OIM. Other than positive and negative relationships between the capital structure (TD and DER) and profitability, this study also finds that TD and DER have positive significant influence on OIM and ROE, but have negative insignificant relation with ROA. Thus, it is necessary to optimize the capital structure by adjusting the target of capital structure that can provide a balance on the marginal cost and marginal benefit
