The present invention refers to pharmaceutical microparticulate compositions of biologically active polypeptides and methods of forming and using such compositions. More particularly, microparticle compositions for sustained release of biologically active polypeptides are provided. By using particular pharmaceutical excipients or their specific quantity, compositions of biologically active polypeptides with desired release profile can be prepared. The microparticle compositions of this invention comprise a biocompatible polymer, a biologically active polypeptide, and pharmaceutical excipients.