The thematic of Digital Educational Resources (DER) and of electronic institutional repositories assumes itself as an emerging trend in Education in Portugal, at the elementary and secondary levels. The wide variety of open content from various sources has led to the design and development of repositories in which DER are systematized. Thus, its availability and scattering are facilitators for the educational community as they simplify the work of teachers who face the existence of a broad range of relevant resources. This paper presents a characterization and evaluation of three repositories with visibility in Portugal, in elementary and secondary levels, using the key dimensions that affect their quality. The factors that may contribute to the improvement of some of the characteristics of the national repositories covered in this study are stated in the conclusions.