A composition for the sustained delivery of a drug comprising an amphiphilic diblock copolymer; a poorly water-soluble drug; a biodegradable polymer; and liquid poly(ethylene glycol) or functional derivatives thereof and a process for preparing the composition are disclosed. When administered into a particular body site, the composition forms an implant containing the drug and drug containing polymeric micelles, which are slowly released from the implant to maintain a constant drug concentration for an extended period of time.