A new two-scale computational strategy is proposed for the analysis of structures which are described up to the micro level, such as composite structures. The description of micro and macro quantities is performed on the interface, arising from the decomposition of the structure into an assembly of substructures and interfaces. The strategy can be interpreted as a two-level mixed domain decomposition method and then is well-suited to parallel architecture computers. Several numerical examples for composite structures illustrate the possibilities of this method. Comparisons with other computational methods are given.