This paper develops a preliminary study to explore the determinants of capital structure of Sri Lankan listed manufacturing and services sector companies using firm level panel data for the period of 2003 – 2007. Profitability, Tangibility, Size and Growth rate were used as independent variables, while leverage ratios such as total debt ratio, long term debt ratio and short term debt ratio were the dependent variables.OLS dummy regression model was used here. The results revealed that only profitability variable was statistically significant with leverage ratios (with total debt ratio and short term debt ratio) at manufacturing companies. Meanwhile all the selected variables, except tangibility were significantly related with atleast one of the leverage ratios in services companies. Results of this study validate the prediction of pecking order theory in the case of profitability variable in both manufacturing and services companies. Also growth variable of services companies again confirms the pecking order hypothesis. However size variable of services companies confirms to prediction of trade-off and agency cost theory.