The present invention relates to a method for preparing an injectable composition of microparticles for the sustained release of a biologically active agent. The microparticles include a biocompatible polymer and a biologically active agent. The invention provides an improved process for the preparation of microparticles, wherein the physical characteristics of the microparticles, for example, the morphology, density and size, are independent of the process used to prepare the initially formed polymer/drug matrix. The method includes the steps of (a) providing a polymer/biologically active agent matrix; (b) compressing the polymer/biologically active agent matrix, thereby forming a compressed matrix; and (c) fragmenting the compressed matrix, thereby forming an injectable microparticle composition. The polymer/drug matrix can be provided by any suitable method.