In this study, drug delivery system of gliclazide, a poorly soluble drug, was developed and evaluated in vitro and in vivo. We synthesized five series of mPEG-PCL di block copolymers. The structure of the copolymers was characterized by H-NMR, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) techniques. In this study, gliclazide was encapsulated within micelles through a single-step nano-precipitation method, leading to formation of gliclazide/mPEG-PCL micelles. The resulting micelles were characterized further by various techniques such as DLS and AFM. The serum glucose lowering effect of gliclazide micelles was studied in streptozotocin-diabetic rats and were compared with the gliclazide treated rats. The results showed that the zeta potential of micelles was about -14.9 mV and the average size was 83.12 nm. Gliclazide was encapsulated into mPEG-PCL micelles with loading capacity of 21.05 ± 0.14% and entrapment efficiency of 94.11 ± 0.12%. In vivo testing of the gliclazide micelles in diabetic rats demonstrated a significant antidiabetic effect of gliclazide micelles after the 7 day that lasted for 21 days when compared with gliclazide powder. The results suggest that gliclazide micelles are a valuable system for the sustained delivery of gliclazide.