Recently, sustained-release injectable microspheres as a novel parenteral administration system have been interested on for many years, due to the excellent advantages when compared to traditional dosage forms: less administration frequency, lower adverse side effects and no need for a surgical procedure. Therefore, major progresses in the development of another successful marketed sustained-release injectable formation have been made, but most investigations are merely limited in laboratory levels; in addition, few reports focus on giving some positive guidance to launch these novel microspheres into market. This review addressed some commonly used polymers, preparation methods and sterilization processes relating to biodegradable microspheres. Moreover, the processes for measuring the sustained-release behaviour of this novel system are summarized in this report, including the methods to determine the in vitro and in vivo release behaviours and the strategies to analyse the in vitro and in vivo correlations.