The objective of this paper is to study the intrinsic determinants of the capital structure according to the firm size. Because of the differences in organisational characteristics which can exist between SMEs and large companies, it is anticipated that the influence of these determinants will differ from one group to another. The empirical analysis relates to a sample of 2919 firm-years listed on Euronext Paris during the period going from 2003 to 2006. The results seem to show that the examined intrinsic determinants, in particular the profitability and the tangibility of assets, affect overall the capital structure of the two groups of firms in a rather similar way (influence direction) but in significantly different degrees (influence extent).