In this study, novel pH-sensitive micelles were prepared from miktoarm star block copolymer, mPEG-b-P(MMA-co-MAA)(2), by the atom transfer radical polymerization (ATRP) technique and dialysis method. Molecular structures and characteristics of the micelles were confirmed by H-1 nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The self-assembled micelles have a very low critical micelle concentration, indicating a high colloidal stability in aqueous solution. Methotrexate (MTX) was selected as the model drug of poor solubility. A relatively high drug loading capacity was found, and the in vitro release studies revealed that about 26% of the drug was released in simulated gastric fluid (SGF, pH 1.2) over 48 h compared to the maximum drug release of about 98% in simulated intestinal fluid (SIF, pH 7.4). Thus, the pH-sensitive micelles might serve as promising carriers for oral drug delivery of hydrophobic drugs with controlled release behavior. (C) 2016 Elsevier B.V. All rights reserved.