This research aims to find out the effect of debt on firm value with firm size as moderating variable on basic industry and chemical manufacturing company listed on Indonesia Stock Exchange (IDX) period 2015 until 2017. Debt, firm size and firm value chronologically are measured by debt to equity ratio, ln total assets and price to book value ratio. This study is using quantitative research, the sampling technique used purposive sampling. The analytical technique used in this research is moderated regression analysis (MRA). The sample of this research is 16 companies out of 66 companies. The result of this study indicates that debt has no significant effect on firm value, but firm size is able to moderate the effect of debt on firm value also strengthen the relationship of debt toward firm value