Capital structure implies particular combination of debt and equity employed by a firm to finance its assets, opearions and growth. Debt comes in the form of debenture or bond issues or ong-term loans, while equity may come in the form of common stock, preferred stock, or retained earnings. In order to achieve optimal capital structure, variables, which affect it, needs to be reviewed including company size; business ris; and profitability. The objectives of this research are: (1) to examine whether company size affects the capital structure of manufacturing companies registered on Indonesian Stock Exchange in 2019; (2) to analyse whether business risk affects the capital structure of manufacturing companies registered on Indonesian Stock Exchange in 2019; and (3) to explore whether profitability affects the capital structure of manufacturing companies, registered on Indonesian Stock Exchange in 2019. The research population were all manufacturing companies registered on Indonesian Stock Exchange in 2019; totaling 149 units. Sampling was done through proportional cluster random sampling. The number of samples in this research were 60 companies. The data collection method employed was documentation obtained from Indonesian Capital Market Directory 2019. The analysis methods used were; descriptive analysis, inferential analysis (F test and t test), determination coefficient and econometric evaluation (multicolinearity test, heteroscedasticity test and normality test). The data analysis was performed through the assistance of SPSS versi 12.0 for Windows. Based on the multiple linear regression analysis, it obtained regression equation of Y = 0.027 + 0.089X1 + 0.007X2 – 0.569X3 + e. Firm’s  size, degree of business risk and profitability have found to affect a company’s capital structure jointly. This is indicated by the result of F test with Fcount = 8.711 > Ftable = 3.23 with probability value of 0.000 < significance level of 5%. The determination coeffieicnt obtained was 31.8%, while 62.8% was explained by other variables which were not observed in this research. Partially, company size affects capital structure, indicated by the result of t test with tcount = 2.356 with probability value of 0.022 < significance level of 5%. Partially, business risk does not affect the capital structure. This was shown by tcount = 0.462 with probability value of 0.646 > significance level of 5%. Partially, there is effect of profitability on capital structure, this is shown through the result of t test of tcount = -3.277 with probability value of 0.002 > significance level of 5%. Based on the classical assumption test, regression equation obtained has fulfilled BLUE requirement since it does not contain multicolinearity, heteroscedasticity and autocorrelation, in addition to the normal distribution of the data. The conclusion obtained from this research is that company size, business risk and profitability simultaneously affect the capital structure. Partially, the variables of company size and profitability affect the capital structure. The suggestion that can be given are (1) Investors who want to invest to the manufacture companies need to pay attention to the capital structure level owned by the company, especially the company size and profitability, (2) Issuers, especially the financial manager needs to be more careful in determining the company capital structure composition by considering the asset or size of the company, as well as the profitability of the company, The implication of this research is that review needs to be done concerning judging the impact of  fundamental factors on thefirm’s  capital structure by adding other factors as well as expanding the observation period so that data accuracy is achieved and estimation is more representative