Abstract: We examine the effect of institutional ownership and voluntary disclosure on cost of debt for the population of manufacturing companies listed in the Indonesia Stock Exchange (IDX) from 2006-2010. Voluntary disclosure is measured using the 32 criteria established by researchers below. The sample of 34 companies is selected from the population using a purposive sampling method. This study uses secondary data from the IDX Capital Market Reference Center in the form of annual financial reports from 2006-2010. Statistical testing is by using multiple regression analysis. This study uses firm size as a control variable. Our results show that institutional ownership and voluntary disclosure have a negative significant effect on cost of debt that is they reduce the cost of debt. Meanwhile, the size of a firm does not affect the cost of debt.